Birthdays

Another question posed to my friends. Here's the issue: Birthdays. I've got an ex-wife who's not friendly or compromising. But I have 2 step-kids that love birthday parties. As they get older, Scott and I struggle with how to deal with these parties. In the past, we've always had smaller parties with our family here in CT, but now that we have a social butterfly (Grace), who's in 1st grade, she wants tons of friends over. Her 6th birthday, in January, her mom had a party for her with about 12 kids. Grace's bday happened to fall on our weekend, so instead of starting up WWIII, we allowed the ex-wife to go ahead with her big party on our day, and Scott and I went to the party. Because Scott and I are the more mature people, this worked out fine. Heather (the ex), took care of the cake and the pizza, and Scott and I brought drinks and snack foods. A pretty decent split. The birthday location was at the Judo place where the kids go, so it was a more "neutral" location. But Scott and I still ended up having a smaller party the next day because Scott's family didn't attend Heather's party. So still, we ended up with 2 parties. As Austin's birthday approaches, we have a similar issue. His birthday falls on our weekend and Austin asked to have a bowling party and so far he has only given us the name of 3 friends. I honestly don't know what the right answer is here. Picking up 3 friends in Newington and driving them to Manchester (about 25 minutes), isn't bad. But what if Austin decides to have 12 kids at his party? Will those 12 kids' parents be OK with transporting them to Manchester? And what about Heather and her parents? Honestly, I don't have a good solution for this issue. If we break it up in 2 parties, does that make most sense? Heather can take on school friends and Judo friends and do a big party in Newington, and we can do a smaller party for our family and Scott's family in Manchester? The more I think about it, the more that makes sense. Of course Heather won't compromise with the dates. She doesn't understand that a child's birthday can fall on ANOTHER day, other than the actual birthday, which means that every other year, we'll lose our weekend with the kids. In other words, take this year for instance. Heather could easily do a big party for Austin the weekend before or the weekend after his actual birthday, but she won't. So if we hosted the big party this year at the bowling alley, that would be fine, but it would cost us a LOT of money, and keep in mind...we have no connection with these kids normally, so getting names and phone numbers is VERY difficult. I actually like the idea of doing smaller parties. Inviting 2 or 3 of Austin's friends and doing something fun, like bowling. And for Austin, that would work out great. he's not really the kind of kid that likes big parties. For Grace, that will be more difficult, as she LOVES big parties and has so many friends. She has already told us who she wants to invite to her Ice Skating party. :) God I love that girl. She's a riot. Anyway, any suggestions?