Who Is To Be Invited?

Hello,
I need to know who all is supposed to be invited to the dinner rehersal. I have 5 bridesmaids (one of which has two kids and a husband- one has a friend that is coming) 5 groomsmen, 3 flower girls and 3 ring bearers. I know that the kids parents have to come but say for an example does my brother`s in-law`s have to join, we are kinda close--- But it`s my father-in-law who is going to be paying for it and he wants to know how many people are coming. What do I do!!!!!! I don`t want to make him go broke!!!
Thanks,
M