i think u can ask for more money in the court... it is not like these r only ur kids u know.
i feel so sorry for he mess and worries u must be in right now.
i really don't know how it is done in here, but in europe, father has to pay for his kids till they start working or till they finish school or become i think 24-26...whichever comes first.
can u take a good lawyer, who wldn't waste ur time and money for this?
i cannot think of any other thing in here.

i have other idea, but... how old r ur kids?
if u know they will not play fair, as in him and his family...play on their feelings. father, grandparents and so on...if u will have no other way.
ur kids have no fault in this whole case and they deserve the best for them. sometimes a mother has to play the situation, for the greater good.

when u will re-marry, and i wish u that u will find a real man for u, just in case, sign a prenup and state all ur needs...just in case. after all, we r only human.

good luck!

If you're looking for a problem, you're probably gonna find one.