Who can speak to back taxes owed by parent with dementia?

It's an Offer in Compromise. If you hire a CPA to do this for you be sure they have experience in dealing with the Collection side of the IRS. Most CPAs do tax returns and do not deal with how you're going to resolve the debt to IRS. Make them tell you how much experience they have in actually getting this type of deal approved. How many have they done? How many were actually approved? Trust me on this... I ran this program for IRS in the state I worked in and have put on a seminar for hundreds of the type of tax professionals you want to hire to represent you.

SJane 1124, I believe you misunderstand the Offer in Compromise or Fresh Start program. The idea is not to lower your tax debt but to resolve it. If the IRS thinks it can ever only collect x amount of the total debt it may settle with you right now for that amount and legally waive the right to collect the rest. The computation for determining that amount may be complex and scary to the taxpayer, which is why they hire third parties to do that for them. It is not about reducing your debt but collecting as much as possible in a reasonable time limit.

My personal experience after not filing taxes (did file an extension to file each year, updated address) for two years during/after divorce was to hire a specialist CPA firm dedicated to practicing before the IRS, the advertised kind who gets people out of trouble with the IRS. I paid the CPA firm $750, did not owe any taxes. If one finds the wrong CPA, they will defend themselves by saying: "All CPA's are licensed to practice before the IRS". That is not the specialist I am talking about.

Experience 20 years later (in 2018) was to refer elderly loved one in Al, to same for tax relief. Advice not taken, family saying it was too expensive!
RESULT:
IRS has attached SS payment monthly, plus penalties. Elderly in an Al!

The mistake here was to talk to the IRS themselves, trying to negotiate.
Do not do that, imo.

Are you talking about federal income taxes? Yes, there is a statute of limitations. No one to talk to at IRS right now due to government shutdown. If there is no income or assets to collect from to pay back taxes just provide that information. If the debt is uncollectible the government moves on to the next case. Retired IRS Revenue Officer (tax collector) here.

We have made every sale of property for mthr with advice from a CPA. Our elder law estate atty is very good, but he is not involved in the taxation end like a CPA is. I'd talk to your CPA as well to find out what exactly can be done on the tax end. The atty is for your personal liability I would think.

Does the IRS have a statute of limitations? I think not. If the senior has the resources or even if they do not, the IRS will go after the owed money. Plain & simple.

Other than hiring one of those forms that work to diminish the tax debt the person will still have to pay something. Those tax firms diminish debt and do not erase debt.

Others will chime in soon re dementia pts having a POA & the POA’s role in overseeing the sale of the property, but I don’t think that will effect the tax burden or erase it.

Sounds awful, and I can only offer sympathy.