I have a similar policy. The don't pay for any time I take off and I have in my contract that I can take off up to 3 weeks plus 5 personal days. They get one week unpaid and everything above that is full pay.

I'm going 4 full weeks without pay from them. My vacation time is reasonable and they could match at least one of their weeks to mine.

I don't have any divorced parents, but I would think that it would be understood that the policies are based on the one child, not the child split into 2 families.

Stick to your policies. You've been nice enough already. Remind them that this is how you budget your year and how you are able to continue to offer care.