How would you deal with an ex inlaw who is depressed and living with an alcoholic?

Almost twenty years ago my ex’s sister and I had a very nice relationship. Over the years she lost two of her children to drugs and had 3 divorces. She is on anti depressants, pain meds and tranquilizers now. Recently she began calling me from out of town. She told me she’s living with her fifty six year old son who went from being a religious fanatic for years to an alcoholic now. He refuses to work or move out and gets drunk and abusive often. She is planning to move near me and my daughter. My daughter used to be her aunt. We both are fond of her but foresee possible or probable stress thinking of her needing rides, various kinds of care and we wish to avoid her son coming over to our houses for fear of him drinking (we don’t drink nor does she). My s/o barely knows her, has never met her son and wishes to avoid them as much as possible. When I talk to her there is nothing we can discuss that isn’t depressing; after all , her brother was my husband and her view of him is more positive than mine. Should I welcome them with open arms or move to another continent? I suspect her wanting to move here serves the purpose of us acting as a sort of “buffer” between her and her son who she fears at times. And her brother (my ex) lives twenty miles away but is always “out of town” when he’s needed for anything. I feel he set this up as a sort of revenge against us; he’s that type and would find it quite amusing. He would not have her over to his “house” since his girlfriend is a true hoarder and he found a possum on his dinette table. It is one scary domicile. I do like her, she’s a sweet, caring lady but I have this avoidance feeling due to her springing the “he can’t stop at one beer” announcement. Sorry this was so long.