Have a sibling that is manipulating my mother (85). I don't know what to do?

No, I think Mom is playing Divide and Conquer. It would be a lot better if you stop letting mom drive a wedge between you and play you two against each other. Set up a nannycam and watch mom complain to her about you. It's a classic move called "Divide and Conquer".

If you are not a party to a conversation, you should not record it unless you have the permission of at least one person in it (in a One Party consent state). If you live in a Two Party/All Party consent state, you need permission from all parties in the conversation whether you are in it or not.

mwl-law

Does sisters ex husband know sister wants to move in or has already moved in? Perhaps it isn't moms decision but ex husbands call on who lives in his property, especially his exwife. Regardless it doesn't sound like mom needs a place to live. She has one unless sister causes conflict. Do you know why your niece wanted sister out? It might give you an idea of what type problem you would have with her. I know you don't think she would follow through on any agreement, but if sister is going to move in anyway, why not draw up a contract that lists what and when sister will do to help mom? How will the expenses be shared? Guests or late nights that would be disruptive to mom. Tell her what needs to be done and what portion you are willing to continue with. Then perhaps you only need visit from time to time to check on how things are going. Take this break while sister is willing to help. If sister is true to course she will probably be gone soon unless she is too comfortable. When or if you see signs of abuse or neglect you can take action on moving mom or speaking with the ex husband for his assistance in getting sister out. Meanwhile two people who need assistance might be able to help one another. I do agree that mom could be playing you but you can rise above it with clear boundaries expressed to both of them. I know we read a lot about dead beat siblings but sometimes siblings come together in spite of parents manipulation. Do you have DPOA and MPOA for mom? Good luck with whatever course you decide on.