First of all, Gunner is an awesome name and I LOVE arbonne!!
Anyway, you need to decide when you want to do his party and only do it on that day. It is understandable to want to do his 1st birthday twice because that is an important milestone. Each year is important, but there is no reason why you have to accomodate everyone else's schedule. You are the mom, you say when it is and tell them now. Maybe they will decide to stay home instead of going away. The ones that will be there are the ones that really care...sounds harsh, but it's true. Also, maybe have his party the saturday before or after the 4th. That may alleviate the vacationers inability to attend. Either way, decide when you want to do it and where and send the invitations. People will come or make sure they can schedule a visit if they want to be there but can't make it to the party. Remember: "no, I can't do it any other weekend; no, I have to have it at X place at Y time; no, this is the only party we will be having, I'm sorry you cannot make it, we hope you can visit at another time."
Take care, Be strong, You're in charge!!