The Hellfire club would be ready and waiting for them. This much they knew. Readiness was the key for when they landed.
Okay, here is the start to the fight with the Hellfire club. Emma/Bobby, Warren, Logan, Remy, Tessa, Morph, Mariko, Mystique, Piotr, and Kitty are the ones we know for sure are on the mission. If you wish to jump in you best do so at the beginning. Just be prepared to have to write a long narrative later on when Selene locks the X-Men into their minds. More info on that when the time comes.