I appreciate everyone's input.
Barb, I wish I could bring mom back here for a respite for my sister. Mom has Alzheimer's and is now at a stage where she is becoming fearful of leaving the house. In fact, just last week, we had a dinner in my sister's dining room, a room that mom is unfamiliar with, which caused her to completely freak out for several hours. Moving her around at this stage in the disease would only cause her a great deal of trauma.
Right now, and since mom has moved in there, my other sister -- the RN who just never seems to have the time for mom and honestly never did, and I pick my mom up on Saturday and Sunday, so my sister and her husband get most of the weekend free, including being able to get out for dinner. My fear is that soon mom will not want to leave the house even to go out with me or my other sister. Then, we can spend the day there with her and allow my BIL and sister to get out, but it won't be the same. My BIL has mentioned several times he's tired of "all the people" in his house. He wants his privacy back.
I hope they can work this out. I really wish they would go for counseling...