Any advice on handling a disagreement with a sibling about the level of parent's decline?

Any person at age 90 or otherwise needs a plan in place for managing finances when the time comes that he/she can’t. It doesn’t matter how competent mom is today, she may not be tomorrow. It’s better to plan while she’s still hitting on most of her cylinders.

By standing in the way of sister’s push to get this done, you may be shooting yourself in the foot. Dealing with management of their affairs would be twice as hard if, say, she were lying helplessly in bed after a stroke and dad’s wringing his hands as you’re all trying to untangle the financial mess so you can pay for the care they suddenly need.

Don’t wait.

Don't wait until mom makes a $20,000 mistake before one of you keeps an eye on their finances. We read a ton of posts here where elders with memory issues appearing to be fine wind up falling for scams by smooth talking con artists.

Why don’t you set up a meeting with Council on Aging. You can both be present at the meeting. Have a needs assessment done and see what they recommend for your situation.

Your mom will need help at some point even if she is doing fairly well now. It’s best to be prepared before something tragic happens.

Best wishes to you and your family.

Be open and honest with each other & parents and stay calm. Have a plan in place because at their age changes happen quickly.

I’ve seen situations like this get out of control and ruin families lives forever

My mom was exactly like that. Then she frittered/was conned out of a lot of money. Before, she could have afforded in-home care. Now, it’s substandard nursing home. Makes me feel ill.

Be careful, things can go south very quickly. It’s a lot easier to have these conversations while your parents are competent. But if they resist, there’s not much anyone can do when it gets bad. I say when, not if. Statistically, neural decline is inevitable with one or both.

Tell your sibling that advice is only heeded when it is wanted. While your parents are still capable of handling their financial affairs, they are legally entitled to do so. While your parents are still of sound mind and capable of signing legal documents, make sure their paperwork is in order. They need to set up powers of attorney for financial and medical matters, if the time comes when they are no longer able to make judgements for themselves. Usually the spouse is the first level of POA, and a child is the second level of POA if the spouse is not capable. There can be conflicts when there are co-POAs, or when one child is POA for medical matters and the other is POA for financial matters. Sometimes it is better just to have one POA, but have backups. They also both need to set up living wills, explaining what their advance medical directives are, and they both need to have wills, if there are assets. They will most likely need an elder attorney to help with these legal documents. I was an only child, and was my mother's POA for both medical and financial matters. I took over my mother's financial affairs when I started to notice that there were late bills and she was not filling out the checks properly. I asked if she'd like me to take over her finances and she was glad to let me do it. At that point, I set up all of her accounts online with autopayment so that I could monitor what was happening.

I think you are BOTH RIGHT if that makes any sense. There DOES need to be plans, paperwork, and you do need openly to be able to talk together with your parents. Be honest. Find out what is what. Keep any anger or insistence at bay. I am assuming you both are in the same area as your parents, and are both seeing them, thus aware of where they seem to be at.

Families vary in how secretive and private they are, but with parents in their 90s it is time to put the cards on the table and at least discuss all of this.
Admire you for trying to honor one another's and your parents positions. I think you will do great despite one perhaps a bit more proactive than the other. So glad of your support for your parents. You're to be congratulated for wanting to work TOGETHER when so many siblings squabble and it all goes South, causing great pain to the parents, and backing them into their corner more than ever.

Good luck. TALK TO THEM after you talk together. Come to a way to approach all this gently and with love. Tell them you no way want to switch roles and would have utterly no idea how to do so, but that you DO want to be support for them, returning the love they always gave YOU.

A family meeting with a banker? A neurologist? A Geriatric Psychologist?

BrundyB: Make sure that your parents' finances are well secured. Smooth and aggressive scam artists target the elder population.

As our parents get older, they do not like to be told that they can’t manage their own affairs as they feel that their freedom to do so is being taken away from them.

Now is the time for you and your sibling to come to a compromise about your parents’ care. Your sibling is right in wanting to have the conversation with your parents about future care, and you are right in wanting to allow them to continue to have the freedom to make their own decisions. What you both should do is to compromise and have the conversation now with your parents about their future care, but let them continue to carry on with their lives while you both keep an eye on them to make sure they are doing everything correctly. Once your parents start to make mistakes in their finance, running of their household, etc., this will be the time for you and your sibling to step in and take control of the situation. In the meantime, please make sure that your parents give you both POA, one sibling as primary and the other sibling as secondary, before their memory problem gets to the point where they are incompetent to do so.