How do we get grandma to cooperate?

My aunt and uncle moved in with my grandma, who is 97, and she is being difficult with my aunt. Nothing my aunt does is good enough but my uncle is the knight in shining armor. Grandma's youngest daughter had been the one coming over and caring for her until they moved out of state. Since then my other aunt moved in and grandma treats her completely different. She won't do anything but sit in her chair all day. Her hearing is bad, but she won't wear hearing aids because you can see them. She has macular degeneration and her vision is getting worse. She was still sewing up until about 4 years ago when her eyesight forced her to stop. She's cranky and gets "huffy" over anything that she doesn't like or doesn't sit well with her. She is constantly watching her watch and making sure that the mailman, lawn people etc are coming when she thinks they should. She has fallen 3 different times and is supposed to use a walker whenever she is up and moving around. The only time she will use it is at home when she walks up and down the hallway for 15 minutes, 2 times a day. When it comes time to leave and go get her hair done, a dr's appt or go to church...... she absolutely refuses to bring her walker and be seen using it. My aunt is at her wits end and doesn't know what to do with her. She feels afraid to try and stand up to grandma because she's afraid she won't be nice about letting out her feelings. Grandma "gushes" on the phone with her youngest daughter and says how much she misses her but then gets off the phone and is cranky and untalkative with the daughter who is taking care of her now. What do we do? I could talk to grandma but I'm afraid she will just be worse with my aunt because my aunt talked to me. We are all just at a loss to know what to do.