Hi
i could be wrong but I’m pretty sure you shouldn’t be affected if your the main carer of the children and they mainly live with you.
Do you get the child benefit for them?
i think he could claim as a single if he has a valid reason for not working but I don’t think he could claim for children he only has part time.
perhaps someone else from this group with knowledge on this could verify that or maybe you could ring tax credits and and ask them but also you SHOULDN’T be giving him any of your money as that’s to feed and look after your children and he should be giving you child maintenance.
the only way that could be turned around is if he won full custody of your children then you would have to pay him and he would then get child benefit and tax credits