Stuck in UK with kids - now what?

I have absolutely no idea how it can turn out.

SIL moved to UK years ago from another european country and settled. Has two sons from different non-UK Citizen fathers. Only one kid is UK citizen.

Problem: Her husband is the only breadwinner in the family because they cannot afford childcare. However, she wants a divorce.

Only livable solution: moving home with the kids.

Concern: if any of the fathers disagree, probably she cannot.

If someone has ever faced this situation, I am curious how it turned out. Thanks for the replies in advance.