There must be lots of forums for parents with CSA payments and they will know what your husband can provide to show he has two children in his household now, to reduce his maintanance payments for his other children. Just don't go onto a forum where the parents with care, are having their childrens payments reduced because the father now has other children, for obvious reasons.
Can I ask another random question then. Can my husband apply for working tax credit, he has ILR and just approved for British Citizenship. He's trying to in essence register himself in the system.
Those who hold a valid ILR in the UK, can apply for low income benefits, but not for Tax Credits because as Kate has said, that benefit has been replaced by Universal Credit for new claimants. UC replaces the exsiting benefits called
- Child Tax Credit
- Housing Benefit
- Income Support
- income-based Jobseeker’s Allowance (JSA)
- income-related Employment and Support Allowance (ESA)
- Working Tax Credit
Exisiting claimants of the benefits above, will, in due course, have their benefits stopped if they are of working age and they will apply for Universal Credit. Or they can apply for UC without waiting, if they will be better off being on UC. Or they might do something that triggers a move to UC, even if they didn't want to. Some who could not claim low income benefits, can now claim UC. Others that could claim the Tax Credit benefits, cannot claim Universal Credit.
Any UC claim would have to be a joint claim, even though you are NRPF, as your earnings and capital will reduce his benefit money, but he now can't claim extra money for you, as the Working Tax Credit benefit allowed.
However, it's the NRPF children we are not sure about claiming Public funds for. Have a read of the two link I gave above, here they are again-
https://www.turn2us.org.uk/Benefit-guides/Nationals-of-non-European-Economic-Area-(EEA)-coun/My-child-is-a-person-subject-to-immigration-controhttps://www.citizensadvice.org.uk/immigration/benefits-services-and-your-immigration-status/are-you-subject-to-immigration-control/There is a two child limit for the low income benefits Child Tax Credits and the replacement low income benefit Universal Credit, but as his ex appears to be the main carer, rather unfairly, that two child limit will only apply to her. There is no limit for the number of children childcare can be claimed for via Universal Credit and Tax Credit, if both parents work, but I don't know how childcare claims work with NRPF spouse and NRPF children.
Child Benefit also has no limit for the number of children to claim for, but read the links about claiming for his NRPF children and whether that will affect their visas.