I'm so angry about this...

It does no good to test until the person shows symptoms. It can be up to 5 days after exposure before COVID actually shows up in a persons system. She could show negative one day and positive the next. This new strain is very contagious but not as life threatening, I hear. Here in the US we can buy a rapid test from the pharmacy but since the latest outbreak, they are scarce.

Keep your children away from her. Isolate them as much as possible. My daughter thought she was getting a head cold on Friday but on Monday she started losing her smell. She was able to buy a rapid test and was positive. Her job required a PCR which she got. She quarantined for 10 days.

I think it maybe time to place MIL since no one wants to be responsible for her care. Which is OK. She seems hard to deal with.

Oh boy.

So. What do you want to do?

There are two subheadings: 1. What to do now, today, this morning. 2. What the heck..?

1. What to do now.
Confining young children to their rooms wearing masks is not practical and probably won't be helpful either. If you're proceeding on the assumption that MIL is Covid +, then your husband needs to set up separate living and sleeping and bathroom areas for her so that she can be quarantined - is it possible to do that in the space you have available?

Masks' main purpose is to prevent the wearer exhaling water vapour carrying live virus and thus spreading it around to other people. Unless you're going the whole hog with hi-spec respirators (expensive and uncomfortable, and I'm not even sure they make them for children) masks won't do much to filter out any incoming microbes and protect the wearer. So don't bother. Open windows if possible (what's the weather like and how high are your heating bills?) to improve ventilation and tell the little ones not to sit on grandma's knee.

If other family members were testing positive, then clearly there is no objection to testing in principle so why on earth did they not test MIL? Too difficult? Is her dementia so far gone that you can't explain to her what you're doing and why you need to? Do you have access to either kind of testing kit?

Is MIL showing any symptoms? Who's monitoring her, and does your husband know what to look for? If he hasn't already he needs to download an app with up to date advice on this.

Day to day care - what are MIL's care needs, and how are they being met?

2. What the heck..?
What has your husband had to say for himself to explain how he thinks it's okay to land you and the children with an exposed 81 year old with dementia in your home?
Have you given your sisters in law a piece of your mind yet?
And how about the brother with whom MIL was resident?

Annat, in your shoes, I would take myself and kids to a hotel.

I would also be talking to a lawyer next chance I got. There is no reason for you to remain in this one way relationship.

Thanks for all your suggestions. Most of the comments here are true. The MIL stays in two of the brothers homes taking turns. She usually goes to the sister's once in a while for a visit. She was currently residing at the other brothers home but that brother would not take her in because he has a condition which he is scared would aggravate if he catches covid. I am more upset that this was not discussed with me and quietly done under my back. Also they didnt bother to test her before bringing her here. Now we have to be worried for the next 7 days whether we will catch or not. And exactly as Lealonnie1 has said, she is already going around the whole house maskless and not isolating, she is in the living room the whole time watching TV and my husband has been loving enough to share lunch and dinner maskless with her so that she doesnt feel bad. Whereas me and my kids are holed up in our rooms in masks, hiding. This is not just one instance, I am always discounted in this house. My husband takes every decision as his sisters say and doesnt even inform me anything about. And this has been my breaking point.

She is the one most in danger if she catches it. Maybe moving her was for HER protection. If she is isolated until she is tested (and/or after 5/10? days of quarantine and no symptoms), you all should be alright. If it makes you feel any better, my teenage son had Covid last January before we were all vaccinated and thankfully, my husband and I never caught it.

I'm making an assumption that since Annat believes in vaccinations the children are under 5 and currently ineligible.
I'm also assuming it isn't as simple as just getting MIL tested, tests are in short supply in much of Canada, in my province they are currently limited to front line HCW and high risk individuals who are showing symptoms.
My third comment is that sending someone off to respite care isn't as simple as placing a phone call, the person has to be vetted, there must be a bed available, and many facilities are under heightened restrictions as they try to keep covid out or limit the spread of any that is already there.

Some of the family members tested positive for Covid....
The biggest slip up was to not have Mil tested at that time.

If the sisters plotted to send her to your place, it could be that she did test positive already, but they could not take care of her. Where is Mil's usual residence?

Get Mil tested.
Monitor her temperature, do you have a non-contact forehead thermometer?
Follow now the protocols recommended for having a Covid positive person in house. Until 5 days are past (or more-up to 14 days). Do you know what the
recommended protocols are?

When and if my dH brings Covid home, I would put him in a motel. Well, at least I will consider that.

If she were to be placed in say, for example, respite care, they would test her, and likely not take her with a positive test.

If she tests positive, the kids will not be allowed at school, being exposed to Covid?

So much to be angry about, and I feel for your difficult circumstances.
Now is the time to put that energy into isolating Mil and protecting others in the household.

Yeah, try 'insisting' a demented elder be 'masked' all the time. May as well 'insist' she act normal while you're at it. Not gonna happen. Not to mention forcing her to isolate is likely to be another exercise in futility, considering you're dealing with DEMENTIA here, hello?

When you sent MIL into your sister's home, you did so knowing the risk involved, since there are several people living in that household, right? Now that those family members are sick, what are they supposed to do? Care for this elder AND the sick family members???

Take MIL out and get her tested, then you can relax a bit knowing her status.

Even if she tests negative, you all run the risk of eventually getting The Virus if you breathe air and leave your home at any time for any reason, let's face it. Same as we ALL do. It's an eventuality we're all facing, vaxxed or unvaxxed. In fact, the vaxxed are facing MORE positive tests than the unvaxxed these days, that's a fact. To live is to face illness every day. Being that you are vaxxed, you should feel better to think you'll face a lesser degree of illness if you do test positive and become symptomatic in the first place, right? That was the point in getting jabbed to begin with, or so we're told. The children face very mild symptoms, if any, that's also a fact.

I personally think you have a bigger problem inviting an angry and aggressively demented elder to live in your home (assuming that's where she lives) & be exposed to your children on a daily basis than you do dealing with potential Covid. Covid goes away in pretty short order while demented elders only get progressively worse.

Best of luck with all of this.

I think you should be more angry that all family members are willing to sacrifice their own health for a person that is aggressive and angry dementia side effects. I don't get it. And i still don't get why the vaccinated are so terrified to get covid. What's the point of the vaccine if you are going to keep living in fear?

The schoolkids' school will probably have covid tests on deck. I don't think you have to worry so much about that. What you have to worry about is now returning her to the sister, and if sister won't take her then she and brother have to find a placement.

Your inlaws are dealing with multiple family members feeling ill and needing to isolate and they felt the burden of caring for your MIL and trying to keep her safe if possible was too much, what would you have them do?
I get that you don't want covid in your home and that it's especially galling that your exposure is coming in the back door through family when you have sacrificed and been so careful to guard the front door, but the reality is that omicron is just so infectious and increasingly pervasive that many very careful people are now testing positive. The plus side of this is that very little children usually have mild symptoms if any, especially with omicron.
I think the problem of covid is just compounding your anger at your husband making this decision without you plus your dislike of your MIL - don't forget this is his mom, try your best to work with him on this.

How old are your children? Here in the US children are very much NOT the ones dying from covid. They are the spreaders.

"Of the 73 million children in the U.S., fewer than 700 have died of COVID-19 during the course of the pandemic, according to the Centers for Disease Control and Prevention. "

Source: https://www.usatoday.com/in-depth/graphics/2021/10/08/covid-19-kids-cases-hospitalizations-deaths/8361479002

You and your husband are at a slightly higher risk due to age, and if you have any other issues (smoker/former smoker, overweight, diabetic, immunocompromised, etc) I think you are right in being upset that your husband made this arrangement without first consulting you, but are over-reacting a bit regarding your elderly MIL endangering your kids. It's the other way around. I hope you stay well and can find a solution that works for everyone.

I would be angry as well.    You probably will have to be forceful in segregating your children from her, and also INSIST that she mask (unless she's on oxygen, and I'm not sure how that would work with a mask).   Make sure she doesn't eat with the rest of the family, even if you have to be very stern and forceful.

This may well come to a direct confrontation with your husband.  That might be forestalled by sitting him down and sweetly lecture him on the dangers of contracting Covid, but it also needs to be very firm in letting him know as well that his mother can NOT come into contact with you or your children.   I would start masking your children just to be on the safe side.   And prepare for a  confrontation with your husband.

Does Canada provide a way to test for Covid in the home?  MIL doesn't sound like the kind of person who would be agreeable or suitable for testing in a public place.

I am so sorry and totally understand your anger. It is very thoughtless and inconsiderate of your husband. All you can do now is isolate her until you can get her tested or enough time passes so you know you are all safe. Concerns for you and your children come before your mil or his sisters. ((((((hugs))))))