On Train, before you enter the last room, make sure that you have invisibility
on, open the door, but do not enter, you can sit and watch them, they don't
react to you, but don't enter the room. You can shoot Xenia in the head with
the sniper rifle. The gate closes, and you then need to kill ouromov. If you
can get Xenia and Ouromov in two consecutive, quick shots, they will both be
dead before you enter the room.