You can’t make him step up, you need to let go of that completely which is hard I know, but will set you free.
And fair enough about not wanting short notice late night contact. He sounds like a child himself, wanting 50-50 when he doesn’t financially contribute and won’t agree to a contact schedule is a joke. If the kids are doing ok with you it doesn’t sound likely at all.
Keep your correspondence with him, maybe offer him to make a parenting plan, have a look at the Cafcass website and make sure you’ve done what’s the courts Would want you to do if you find yourself there but it really doesn’t sound like that’s likely to happen.
The other reply is right-, what do the kids want? What would you like? I don’t think you’ve really got anything to worry about from this guy apart from being let down and hurt, sounds like that’s the main thing you need to address? To try and let him go, accept that’s what he is. It’s very sad.
Beware of the lawyer winding you up about court action and making it out Like it’s not a big deal, I don’t imagine you are going to need to go to family court from what you said but lawyers can definitely shit stir, even ones from domestic abuse charities (dare I say, especially ones from domestic abuse charities).
hold your kids tight, they’ll be grown-up before you know it. This time is precious, tried to stop his flaky behaviour tainting it