Am I legally required to file mom's taxes?

Thank you all for advice! I haven't consulted an attorney, but will see if I can get a free consult somewhere. In order to claim my brother, mom needed his SS #, so mom could claim "head of household" and reduce her taxes owed- per tax preparer. (Tax preparer tried to find deductions, and did claim her rent payments.) I believe mom's SS was included as income, as it's part of her total income for the year. (Mom had no debt.) However, my (unstable) brother was never going to give it, nor was he open to discussing it with me because he doesn't believe if paying taxes! (which why he doesn't work) My attempt to discuss it with him, got me shoved out of the house by him.
It seems mom's income totals just over $40K (2 pensions + SS). My (deceased) dad's pension isn't taking out enough tax, which is the problem. He was a federal employee. All I did last year was change the status from Married to Single (which deducted $25), cause I was afraid she wouldn't have enough for Care Home cost. I'm not authorized to make any more changes to Dad's pension withholding with mom's condition. I was so grateful to find a CH that would take her small budget which includes supplies & taxes, which is her entire income. I will definitely contact the Tax preparer after Tax season to maybe file an amendment.
Thank you everyone for the solid, sage advice and for taking the time to respond so quickly and give me the peace of mind to know what I have to do.
Lots of Hugs & ALOHA to you all!

Are you legally required?  It doesn’t sound like you have legal responsibility but you have set a precedent by filing and paying the previous returns. Plus you have your name on her money. 
I think you would need the advice of a certified elder attorney to advise you on your legal status. 
To recap what I think I understand. 
It sounds like mom had enough taxable income and no valid expenses so that she ended up owing taxes.
Abusive son was taking the money and she wasn’t filing her taxes.
Daughter got involved and got mom caught up..,until now.
Mom was living with her daughter for a few months and daughter had the ability to use her mom’s income to pay her back taxes and to save some for the future. She’s not medically qualified for Medicaid. Now she’s concerned that mom won’t have enough money to pay her day care if she uses the money she has saved to pay off this last tax liability. 

I say last because next year mom should be fine because she has the write off of the care home expense and the day care. Mom didn’t have that expense before Feb 2018.

I would still take another look at claiming brother as a dependent as he was a qualifying relative if he was not working while he was using mom’s money. 

Make a phone call to the CPA if you think that’s a possibility. It might reduce the bill a bit. If brother was employed it wouldn’t work. 

You’ve done such a good job getting your mom’s life back on track NAIA. 

I’m sure you already know the IRS penalties involved as you have just paid them for the two previous years. 

One thought is to go ahead and file and then file an amended return if the CPA comes up with qualifying exemptions.

I’m sure you’ve already done this as well but check with your local Area Agency on Aging to see if they can offer any advice or services on how to meet any current or anticipated expenses for mom.

How is your mom doing now? I hope she is less worried about your brother these days.  

Again you have done an amazing job of rescuing your mom and finding her a home. Trust that you will find a way to get her the services she needs when the time comes.

There really isn't an issue here, just angst. Just pay the taxes, is my advice as a retired IRS Revenue Officer (tax collector). And I agree, fix whatever the situation is that is causing this debt. Yes IRS can take her pension, Social Security etc.

If she owes the IRS, agreed, she needs to pay. The IRS will load penalties on and I believe they can garnish her pension.

The thing is, how can she owe 2K? Make sure, by going over the returns carefully with the Tax Preparer, that he's not counting her SS as taxable income.

Or is the issue that she has 1099s from written off debt?

Going forward, figure out how to not end up with a big tax bill next year, by adjusting her withholding or increasing quarterly tax payments.

Assuming the tax preparer has done all possible arguing and negotiating, you'd better pay up.

I appreciate what you say about feeling that her money would be better spent on her care. But quite honestly, the likely costs of her care are going to dwarf a couple of grand before long anyway - withholding the current liability is not going to make any difference to speak of, and will just land her in unnecessary legal soup.

I see by a previous post that your mom was living with your brother and paying the bills.
So you had the few months while she lived with you between her living with your abusive brother and the care home to build her savings. 
Could she claim your brother as a dependent for the time she paid all the bills? Was brother working then? Do you have proof he was living with her and she was paying the bills? Was his name on the lease or just hers?
Are you already working with a certified elder attorney? You might run it by the attorney. 

Mom went into "CH"? Care home?

Is that a deductible expense? Is Day Care a deductible expense? 

Is tax not being withheld from her pension?

I'm trying to figure out how some on SS and a small pension could owe nearly 2K in taxes?