Elderly mother wants daughter and family out of her home. If they don’t politely get out what do I do?

My dad died a year ago and my mom did not want to stay alone so she let my sister, my sister's daughter, husband and child move in to her home. It was convenient for them as well because they had just lost their home to foreclosure. I knew this was a mistake letting them move in and I told my mom but she insisted she needed them there to help her get over her grieving. Well, they all have been there over a year now and during this time none of them have offered to pay a dime to my mom, no rent, no utilities, no expenses. I know this because I take care of my mom’s finances. They can afford it because they all have well-paying, respectable jobs. They are just using her but my mom won’t do anything about it. During this year my mom has contacted me many times about verbal abuse and bullying. They tell her if you make us get out, you won’t get to see your grandson, or they’ll say we don’t have anywhere to go, or we don’t have enough money to get out. I know this is all bolony and so does my mom but I can’t make my mom tell them to get out of the house even though I have told her to tell them. She says she is too afraid to tell them to get out for fear of what they’ll do to her. I have asked my mom, what do you mean and she says they are rude and talk ugly to her. This week my mom had another run in with them. Because of this situation I do not speak to my sister, so I spoke to my sister’s daughter. I suggested to her it might be time for them to move on because mom is considering board and care and will need to sell the home. Well, she threw a fit and hung up on me. (BTW, this person is a teacher.) I called my mom back and said mom you need to let them know that it’s probably time for them to start looking for a place because you want to sell your home and go to board and care. So, yesterday my mom took my suggestion and told them she would like it if they found another place to live. They are again bullying her into thinking they will have no place to go and what about your grandson and on and on and on. So next week, I am flying out to try and resolve this. If they don’t politely get out what do I do? My mom will be too afraid to stay there with them alone now that they know she is trying to get them to move out.