Ok, first question. How would you prefer to spend your holiday?
I wont be back to see your answer for awhile but I think that is the thing you need to work out in your head. Ignore all the guilt tripping (though thats something you probably need to be working on with them) and pretend they'd both be fine with whatever decisions you'd make, write out your ideal scenario. gf going with you to bf's family something you want but not doable? write out your ideal scenario that is possible in reality then
Think about that for the rest of the day and see how you feel about what you've come up with.