I've posted about this before but I don't know how to link to the threads.
An update: After finding out DS abused his ex and children, we decided to send her a letter and a cheque. We wanted to compensate some of the money she has lost due to our son's behaviour. She has posted the cheque back to us but not the letter. I can only assume that she wants nothing to do with us after everything.
Our son is moving in with a girl he has been seeing. He is continuing with court proceedings and now admits that it's mostly about "winning" and not the children. His son is still refusing to spend time with him so we are likely to never have a relationship with our grandchildren.
No advice needed. It was hard reading people's comments and I now realise how blind I've been and what that has cost me.