Take it from one with experience - you can't make another person be a good parent and it's futile and damaging to try!
but it feels like he just can't be arsed but won't say so
This is exactly what's going on!
He won't come out and clearly say he doesn't want to be a parent any more as he would (rightly) be slated so he's doing this crappy man thing where he makes it more and more difficult for you then when you set boundaries (again rightly so) he'll be all "she's stopping me seeing my kids"
Don't be me
Don't play his game!
Don't pursue him for contact arrangements, at most let him know when the kids are available for contact ONCE and once only and then leave the ball completely in his court.
Basically "give him enough rope to bang himself"
In all likelihood he'll quietly and gradually see them and contact you about them less and less - sorry.
Court etc is imo simply delaying the inevitable (and can now be bloody expensive!) I did all that (back when legal aid was far more easily obtained), made no difference to his attitude. He said all the right things in court in terms of 'yes I want to be an involved and engaged parent' but his actions didn't reflect this and this resulted in repeated returns to court plus when he did have her he didn't care for her properly and I'm not talking niggly stuff but eg feeding her things without checking re her food allergies, not giving her meds (asthmatic), leaving her far too long between nappy changes, not dressing her appropriately for the weather (eg sandals in Nov in pouring rain!)
It's extremely common.
Don't get the kids hopes up, if possible don't even tell them if contact is arranged then if he flakes they don't even know. Don't do that thing so many of us (myself included) do of thinking "not speaking ill of the other parent" also means not letting them learn who he really is and seeing him honestly.
Keep it bright and breezy if it comes up 'well you know what he's like now what shall we do today/what shall we have for dinner?' Type thing - though if they want to discuss further let them without making them feel they have to place on a pedestal a parent that's letting them down!
It's tricky I know
Like you I thought I was doing right by dd bending over backwards and constantly chasing to enable contact to my and her detriment and even financial cost. Eventually dd "twigged" and caught her dad and I out in a lie where I'd covered for him cocking up and therefore missing an arranged contact.
She actually sat me down (one of those cute scenes where a kid behaves and talks as they think an adult does) and said she didn't want me to keep almost breaking my own back to facilitate his relationship with her.
Partly she could see the strain it was causing (even though I tried to hide it) partly as she was starting to see her dad honestly, partly as she wanted to give him the chance to show her he COULD step up - sadly wasn't the case, within a year he'd stopped even phoning her and had blocked me from all communication and had started blocking her from some too.
She was early high school stage at this point.
In hindsight it was clear when we first split and she was a pre-schooler that he wasn't arsed to make the effort, we were for the first few months literally within 10 mins walking distance of him and even then he'd be late, cancel last min or just not turn up etc
I should have let him go on his merry way then it would have been much easier on dd in the long term.
Having him fuck off out of her life just as she was entering her awkward teen years was the worst possible timing and even if I could have continued facilitating things i strongly suspect he'd have withdrawn at this point anyway - dd was entering that stage of no longer blindly accepting his excuses and he couldn't cope with that at all! Plus he had other stuff going on that was distracting him (marriage rocky, fell out with his mum etc)
Wow! Well as he was abusive to you I think they're better off without him in their lives anyway
@LouiseTrees Given he's aggressive type I suspect in order to not have him kick off!