I've been playing GTA IV, The Ballad of Gay Tony, and I need help on the last mission! (Departure Time.)?

Have the RPG, grenades and auto rifle with you. As they come through the door fire your RPG or Grenades is it helps to take out big groups at a time if they're close to each other. Blind throw grenades so you won't be hit as you line up your throw. Even through its hard, try to keep track on advancing goons so they don't surprise you and spray you in the face.