Thank's UncleScratchy! I got him.
Although, I found a way to have my party members aid me in the battle. You just have to place them all at the southern wall, and pick them up before the battle begins. 'Cause he can't see you down there. Like you wrote.
It is a little dissapointing, that you can't see all the changes after the Enclave's fall.
Like seeing that new city your tribe built, and seeing Broken Hills in ruin. Stuff like that, I would really have liked to see.
Btw, I used a small gun, The Gauss Rifle. Damn it's good!
Thank's again, UncleScratchy.