Just caught up on this. What a completely disappointing resolution. Three months notice is laughable and frankly embarrassing.
That poor mum and those kids. Likely having a tough Christmas where she's had to scrimp, save and likely borrow to afford presents, food, etc. And then there's OPs son, sitting in his nice warm house with his parents who won't acknowledge what a waste of oxygen he is, giving him presents and a lovingly prepared dinner. I'm sure OP will be in giving his room a tidy and fresh sheets for the big day as well.
See all this utter BS about 'small steps'? It's just excuses, isn't it? You don't want to accept that you messed up (by not believing her). You don't want to admit your son is a disgusting human being. You want to pretend your little family unit is perfect. You want to continue the narrative that his ex is a horrible bitch who won't let him see his kids and he's doing so much fighting to see them.
You are doing those kids a massive disservice. Stop talking about your feelings. Honestly, your feelings are irrelevant in this. The only people's feelings who matter, are the kids and their mum. I can't imagine how scared she was when he laid his hands on her. How scared the kids were when he tore up rooms in a rage. It doesn't bear thinking about. But here you are, thinking about yourself and your feelings and how you 'can't believe it'.
Stop being self centred. Kick him out. Apologise to the mother and expect nothing from her. Prove to her over years that you are worth being in those kids lives. Stop thinking about yourself. Those poor kids will grow up wondering why they weren't good enough for daddy. Why their daddy didn't love their mummy. Why their daddy hurt them and their mummy. They'll not receive gifts on Christmas and birthdays. They'll struggle. Their mum will have to say no to school trips, hobbies, birthday parties- all because their dad won't provide for them.
You'd get respect from me if you came on here saying 'I feel so awful I didn't believe her. Those kids deserve better. How can I make it right? I'll do anything for them". But, alas, no.
I'm not sorry this is harsh. You'll maybe read this- but you'll ignore it. You'll continue to think 'my poor boy'. You'll never kick him out. You'll never see your GC. You'll defend him no matter what mess he gets into, and you'll bail him out. He'll manipulate you to get what he wants. And you'll sit back and let him do it. All you've said on this post are empty promises.
Those poor, poor kids. Their poor mum.