The vampire guys? Talk to them or just kill them. He's in a room that has a computer terminal outside.If you kill them you have to hack the terminalIf you convince them they release him and the top guy gives you the scamatics(sp?) to the shiskabab weapon thing.
Not the vampire people, the people in the subway, past the ghouls (not feral), past the mirelurks and traps.
The Family is the vampire people...
They will also teach you how to get more out of blood packs if you go back after completing the quest.