Are we legally responsible for the repairs or any fines on my mother-in-law’s house?

My mother-law passed away some 20 years ago. Her youngest grown son with his children into move her house in a year before she passed away. He was executor of will, but did take responsibly. But his family scattered in the house all these years. His father passed away some 10 years ago. His youngest son just move out, walking away after 20 years after moving in, 19 years after she passed away. He said he got a notice the roof needs repair. He cannot afford it. They never paid taxes or took care of the house, just live there. The house is still in both grandparent's name. The house is in very bad shape maybe condemned house. Taxes are overdue. The house is going to be fine for run down condition over roof or condemned house. We cannot afford the house in any way. We have our own bills and own house. The house never went in probate or anything else. They always claim the house was theirs. I just got a call from husband's son he said they drove by and the one side of the brick-wall of house collapse onto the sidewalk between the houses. So it might not be roof reason at all.