I agree with Glenda that this should be your daughter's party. There will be more older siblings than her own guests! If you have not sent the invitations, you are the host and you can feel free to say it is girls only.
However, if that is not possible for you, or if you feel you would have too many hurt feelings among your friends, then I think you'll need to arrange to have a couple of the dads take the boys out! A movie, a bouncy place, McDonalds, even the local park. If cost is an issue, there is a cinema in Plano at Coit and Park that shows movies for $1 per person or an ice cream and playland at McDonald's is about the same. Lowe's and Home Depot often have a craft that kids can put together in the store. It takes about 30 minutes or so, and doesn't cost anything, plus the boys get to take home something they made. You might want to check with your local stores to see if they have any activities scheduled for the day of your party.
Good luck! I hope your little girl enjoys her special day!