Lizzie, .... GO! Make the trip. Trust me ... they WILL survive without you! You do NOT need to be involved in EVERY event of your family's life! And don't beat yourself up for wanting some "alone" time or feel you have some kind of "obligation" to them.
Your kids are grown. They are adults. They should be making their own way in life now, raising their own kids, dealing with their own problems. They don't need you.
Your parents and all those older folks? They've made their decisions in life. They are were they are. They got there without you, and they will continue without you. Let them deal with their own problems. You are not their saviour. More than likely, they really don't even want your opinion.
About all those birthdays and graduations and baby births and events? Do YOU REALLY need to be there? Send a birthday card, send a graduation card, look at the baby pics on Facebook. You REALLY do not need to be involved in EVERY event.
Pack up, go! and let live YOUR own life for a while! Everything will still be there when you return.