Lien after husbands death

Hi I have a situation where my husband that  has passed away died owing back taxes and they placed a lien on his house in 2010. When we found out he was terminally Ill we consulted an attorney and drew up papers giving me survivorship rights to the deed. I have continued to pay the mortgage payment that is in his name for the last almost 6 years. We were in fear that if I were to notify the mortgage company of his passing and try to switch the mortgage into my name that this would count as a sale and cause the lien to come due. I am also in fear to bring my intentions to the irs that after discovering the details of the situation that they can force the sale of my house. But I would like to finally have the mortgage in my name. I did not file joint with him. In fact we were not even together yet. What should I do?