@twattingtwatface
What I mean is do I just get school uniform for my days and not buy it for his, because I know the week school starts it will be "I forgot to get uniform, dc needs to wear the ones you got and I'll get some soon" etc.
Do I just get presents from me and if he doesn't get anything then it's on him.
I just know dcs will be the ones to miss out but I don't know how else to change it.
Hopefully the shame will kick him up the arse to finally get his shit together?
I think you draw the line by doing what is needed to meet the DCs' needs and meeting the shortfall of they will be unsafe/neglected otherwise without compensating for him to the extent that you're trying to conceal that he's a shit dad, but not doing things to spite him.
If the DC are to have a healthy relationship with him that has to come from him, you can't orchestrate it. They need you not to minimise or normalise shitty behaviour from him so that they understand it is not ok and don't accept being treated badly by others or repeat the behaviour themselves.
This may mean they experience sadness and hurt. You protect them by supporting them through it and helping them build positive self-esteem by understanding that dad's behaviour is not their fault.
Whilst I understand the urge to "protect" them by minimising ( "oh daddy didn't really mean ") or covering up for him, doing that leaves them unprotected and means they can't protect themselves from shitty behaviour and may build him up as a superhero who's being kept from them by you (rather than the reality of being able to understand he's a lazy rock and it's not ok to treat people like that and no reflection on them).
Providing clear age appropriate information when somebody treats them poorly - so that they understand it's not ok to behave like that, they don't deserve it, and it's not their fault - is not the same as "badmouthing" someone. Badmouthing would be if you vented to them about what a duck he is and how much you hate him when he's pissing you off.
Explaining that it was wrong of daddy not to send a birthday card, it's not a nice way to behave and it's not their fault - that's necessary to protect and support them, not badmouthing. His discomfort about the truth of his poor behaviour still doesn't make it badmouthing.
So you make sure they're fed and clean if he's not capable of doing that, but you don't buy birthday presents for them from him (but do provide emotional support and age appropriate information if he doesn't).
School uniform - you get what they need for start of term and for their base with you. You make sure he has the information on what they need, by the school having his contact details to send information directly instead of via you (once). You answer questions on sizes and things If he asks.
You do not pre-empt his failure by buying extras for him in advance (unless he asks and you agree), you do not chase him or act as his PA, you do not act as the relay for school info he receives directly. If/when he fails, then you step up to ensure their needs are safely met and they understand it was wrong but is not their fault, etc.
Birthday parties - you arrange a birthday party, send invites, make sure he has the opportunity to be involved if he chooses and make sure he knows when it is (and you don't deliberately plan it when he couldn't attend).
But you do not chase him to do things, you do not pick him up and drag him to attend, you do not buy presents from him.
Hospital appointments - you make sure they're arranged and they attend, and you make him aware they're happening (even though it's irritating that he doesn't care).
You do not chase him to engage with what's happening, try and force him to attend, collect him to bring him, or put the children in a position where they miss appointments because of him.
If they get upset about his disinterest, again you provide honest age appropriate information so that they understand dad's behaviour is not ok but it's not their fault or because they've done something wrong or are unloveable.
That's where the line is.
You will have to do more than if you were in an equal partnership, but you don't try to do things for him to conceal his shittiness or do things to score points because you're (understandably) frustrated.
Experiencing sadness and distress are normal parts of life that you can't and shouldn't try to shield children from if they are to live healthy lives with good coping skills - sadness and disappointment are not damaging to a child when they are supported to cope with the feelings and given clear information to make sense of it. That should be your focus.
In the absence of information, children understand the world very simply as "a bad thing has happened, I must have caused it, so I must be a bad person". That is how children and up with negative self-esteem in these situations if one parent is shut and the other minimises instead of being honest. If dad disappoints them and you say "oh daddy doesn't mean it" or "oh daddy doesn't realise this would upset you" it makes them feel it's their fault for being upset and that they're useless/broken, if mum says it's normal and they are wrong to be upset. Iyswim?
That's why it is so important to very clearly and consistently explain each time he does something to let them down or hurt them that his behaviour was wrong and that it was not their fault. You can't conceal it from them but you can protect them with this approach.
They need to hear that from you.
Hope that makes some sense!