J.R.
I don't have "friends" parties for my kids until they are in school so you could just do the little one's with Daddy's birthday.
One thing you could do with the other 2 kids is just pick a weekend for each of them and have their parties with their friends and then have a "Grandparents" party all at once.
I have a daughter that will be 4 on 2/6, son turned 2 on 1/25 and our daughter we are adopting will be 7 on 2/2. The 4 and 7 year olds are special needs so they'll always have a party together and we'll just have a seperate one for our son. It's much easier to have the 1 "Grandparent" party though. Just have each of the kids pick out a 6 pack of cupcakes that they like for the Grandparent party. They love the rings and things that are on top of them so they never complain about not having a cake for that party.
Good luck,
J.
Mom to 4, soon to be 5 through another adoption :o)