I think it should work as a "Arrive" at this time. And just base it off posting order? Who ever post first, gets first dibs.
I have no issue being first or fifth, everyone is there for the same reason. They were invited to partake in a gangbang. I'm assuming all the characters know of HER specifically, not necessary one another.
My guy for example knows she has a few guys she is fucking and doesn' care, he is not in any sort of relationship. I do see him more of a "daddy" type who also enjoys watching and fulfilling her kinky little fantasies but we don't have to play into that. (This gangbang being one of them)
Again, knowing this is smut based, I am not looking to mix in to much plot)