I’ve only just found this thread. What a difficult dilemma for you Annie. On reading through the thread I realise how difficult it will be for you to move, but I think if you do, you will be happy with your choice. Leaving the place where you feel close to Catherine will be hard, but you will take her with you wherever you go, you will always have your memories of her, they will never be lost, wherever you live.
I also realise that you will miss your beautiful mountains, but you will be exchanging these mountains for the love and companionship of your daughter, who understandably wants you near to her, so she can see you regularly and help you if necessary.
Your SiL sounds a strange one, very controlling, but if he never sees you anyway, he will have little impact on you. As long as he doesn’t prevent your daughter from seeing you, even if it can’t be every day, you probably don’t need to worry too much about him.
I do understand why your daughter wants you to live near her. After my lovely old Dad died some three years ago, and the following year, my Mum’s sister, my auntie died, I wanted Mum to come to live near to me, where I could ensure she wasn’t lonely, and had help when she needed it. I do have a sister who lived near Mum,she she is mentally ill and unable to offer any support to Mum. Anyway, Mum moved down here some eight months ago, and is very happy, no longer lonely, and we can help her as necessary. It was absolutely the right choice, and Mum is very happy. Several of her adult grandchildren and nieces have visited, as I’m sure your grandchildren will do. You can look after them wherever you are, as they are adults. You can phone, text, FaceTime them, and keep up with their lives as you promised their mother.
You will have more support, and the love of your daughter Annie, if you move.