They are in the room with the objective, close to the evacuation, and they have all of the entrances blocked (Lighting Claws and Thunder Hammer are really good combined with the Guard stance, and some buffs from cards).
Using my own cards, I managed to take out the Heavy Weapons Bearer carrying Assault Cannon, as he risked having only 1 tile of Overwatch. I got him with my last Genestealer in range, with his last AP (and I still had 66% to win).
After that I managed to kill the Librarian with this new Genestealer Biomorph type - Reaperfex. They are OP as fuck, because they can go through occupied squares and have 8 AP (regular Genestealers have 6). I basically teleported through the closed door to an unoccupied square and engaged his Librarian from the side.
Honestly I don't like this Biomorphs at all, as they unbalance the gameplay too much in my opinion. Thankfully you can only have a limited number of them, you have to convert a blip with 2-3 Genestealers, and if SM player manages to gain LOS on the Blip when it's converting, it automatically vanishes.
On the next turn I try to attack Brother Apothecary from the rear. He already managed to resurrect his Sergeant once, when I managed to win a melee (that's the Apothecary's ability in that game, it's a roll with 50% chance of success). He defended against both of my attacks this time
With my last action I decided to attack his buffed Sergeant from the rear. This time lady luck is on my side:
And 3rd kill secures me the win. After that I got the message, that the host has left the game