Gran32 I have been in your position with both of my DDs so I know where you are coming from, however I do think that you have been overly involved in your DDs marriage and subsequent divorce.
To you it all looked lovely, but it wasn’t.
Your DD wanted to go to counselling but her husband didn’t.
Again, we were in the same position.
Our GCs also split their time between households and are fine.
But all the way through this we kept our lives and theirs separate, I don’t understand how you can be so involved in your DDs life that You were the one who had counselling and they didn’t!
Step back, stop funding your daughter and start to enjoy life with your husband, your daughter will be fine, she is a grown up and if my daughter is anything to go by she will get through it without any more help.
I know it will take a big gulp for you to step back but you cannot control what your daughter does any more (as you have found out).
Take pleasure in your Grandchildren and let their parents sort themselves out, without your help and please stop thinking that your SIL was so perfect, because he wasn’t perfect for your daughter.