I Had the same issue with my Grandmothers estate. She dies in 2003 but my Aunt and Uncle neglected to file taxes or settle the estate so the IRS sent a letter to them in 2004, 2005, 2006 asking about tax filings thinking she was still alive. They never told anybody else about it. Found out when I went to my grandmothers house to check on it after a storm. A neighbor told me the IRS came to talk to them about my grandmother. They told them she passed away but periodically family would come to check on the house. The agent gave them a card and I called them. That was when I found out the Aunts and Uncles did nothing. Agent told me what needed to be done. I told Aunt and Uncles what the IRS said. They told the government cannot get money from a dead person and refused to do anything. IRS initiated proceeding against them and I was a witness. The IRS told the judge I was at least acting responsible so he gave me fiduciary duty to file back taxes and settle the estate. Finances were a mess. Took my over a year just get the all the financial information to file the taxes. Since she had a trust I had to file 1041 for the years after she died. Found out my Aunt and Uncle were "acquiring" money from her accounts before and after she died. When I settled the estate I filed a report with the court which a copy was sent to all family members outlining everything I found including the amounts taken from her accounts by family members. Needless to say it cause a huge family split.
The IRS will work with you if you have the right attitude.
PS. Because the way my Aunt and Uncle acted toward them the IRS went after them for back taxes on the money they took which was 6 figures.