I'm standing in the surrogate grandmother line and tossing you a few towels to hang onto Carsam. That bundle of Joy has to be your first focus. What a wonderful time for you.
As for your grandmother. There is nothing you can do to make it any different than it is. Yes, it will be worse and then it will be over. Your Uncle has decided what he must do and yo have to let him finish his choices.
As for your Mom. My daughter had a come to jesus meeting with me not long ago. I know she loves her grand parents but she loves her Mom more. I am allowed a limited amount of time to talk about my parents, I am not allowed to talk about the sister chaos for more than 5 minutes. Then it is our time. We talk about her school, her work, what I am doing other than my parents, and anything else we want to. When we are together we spend time together not time rehashing family chaos. It has become the time that I cherish more than anything. But it was her being directly and brutally honest with me that made me realize how obcessed I had become. So take Mom out to lunch and tell her up front that there will be NO conversation about family affiars. Better yet, take her baby shopping. You can help her refocus. She has a mother with ALZ but she has a daughter that is pregnant. Sometimes kids do give the best advice... I know I listen to mine now
Congrats on being pregnant. Try not to worry too much about what you can not change. Then make the changes that you can. You can be the start of something better.