In the mission, End Of The Line, Father tells you to eliminate the railroad, so i went to the HQ and I killed everyone but the quest did not complete, then I remembered that I sent Deacon to sanctuary after I found another companion, so I went to sanctuary and he won't take any damage. Any ideas?

You've made four threads about this man, I don't think anyone knows. We all just started playing the game two weeks ago, and there are bound to be bugs. This sounds like one of them.

Can you kill him with console command? Try it. Maybe it will fix for you.

maybe dismiss him as a follower or settler.

ill try that