I need more details, dude. If I hung out with them for a year, would a new me appear or would we all grow older together? In the case of the latter, would a new 1 year old me appear when the previous 1 year old me turned 2? These are important considerations!
I assume this is a multiverse situation, and at the end of the party they go back into their normal timelines, only with the experience of that gathering now with them.
No changing the past for yourself, but maybe changing the course of all of theirs based on how they react. With that in mind, I can't think of a single thing I'd say that would help any of them, except maybe:
"Let's all work on figuring out how this happened, because this rather breaks the universe, doesn't it?"
If it was a bootstrap paradox situation, where everything that happened happened, then you'd start to get some serious temporal feedback loops, like some mics too close to a bunch of speakers.