What can be done if we have put the house on the market and his sister will not get out?

I have a brother in law that has power of attorney. My father in law passed and he had a reverse mortgage on the property. When a realtor goes to show it, she won't let them in. She also took the sign down. We are trying to get some money for the rest of what’s left and it is to be divided to all 5 after the reverse mortgage is paid. She has signed my father in law’s name for the past 8 years saying he was residing there. He has not. She refuses to leave and has never paid any money. Her father has asked her to when he left that house 8 years ago. He passed away and left a living trust that states to sell all split the left over money 5 ways. If the house is not on the market or has not sold in a certain time, they can lose all from foreclosure. She stated she will lose it before anyone gets a dime. She is very upset that her dad did a reverse mortgage. She has never paid anything there at the house when her parents were living.