So you have a family of 2 adults and 2 children. CTCs applied for and paid for those two children. Parents split up, one leaves. The RP will get the CTC for the 2 children who are based with them.
The NRP goes off and doesn't get CTC for those 2 children.
Now the NRP meets someone else, gets remarried or whatever, and has 2 more children. This family, Family2, claim CTC for their 2 children. Then the parents split up and original NRP goes off again, leaving RP2 with 2 children for whom RP2 claims and gets CTC.
NRP then gets together with yet another person, has 2 more children, and Family3 claim and get CTC for those 2 children.
Meanwhile, RP1 has met someone else, they have been together 5years now and have 2 children together - Family1.1
So Family1/1.1have 4 children living with them permanently, for whom they bear the bulk of the costs and do the bulk of the caring. They get CTC for 2 children.
Family2 - RP2 - has 2 children, gets CTC for 2 children.
Family3 has 2 children and gets CTC for 2children.
NRP does not get CTCs for any children unless NRP is actually living in that household and therefore bearing some responsibility for those 2 children who live there.
If NRP were to leave Family3 the CTCs would not leave with them, the CTCs would remains with those 2 children and RP3.
Have I got that right?