Child Benefit Charge

Husband (H) and Wife (W) got divorced last year. They have 2 children who live with mother (W). The divorced husband (H) provides maintenance for W and kids. H earns over £60K. W is in a new relationship with X who lives with W. X earns over £60K. H is also in a new relationship with partner Z. W earns less than £50K.

Who suffers the High Income Child Benefit Charge (and has to fill in a tax return)? What if X also supports his own children and wife from a previous marriage? What if Z earns <£50K and also has children so you have another household partnership of H and Z?

Feedback welcome. Thanks.