Vacations are hard for everyone! You just need to do the best you can. If you journal your food, write down everything that you eat to help reign you in if you start going overboard.
Will you be bringing any food or doing any cooking at the barbeques? Prime time for making sure that at least some of the food available is something you feel comfortable eating.
One thing you do not want to do is to tell people you are trying to lose weight. The standard response always is "You're on vacation, live it up!" It's too easy to agree with that and then just binge all week.
Just make your choices and keep them to yourself, then enjoy the company - which is the real reason for the trip, not the food