I've been unable to complete the We Will All Go Together quest. The arrow which points to the last feral ghoul or his irradiated dogtag points to a spot between two buildings near the church with the NCR supply depot.
I've reloaded to before obtaining the quest and the arrow points to the same spot again. Either the ghoul is under the world or the pathing to the ghoul is broken. I've searched and cleared all the ghoul corpses in the town to no avail.

the last ghoul is in fact inside a house with a doorway that is in an alleyway-

he is actually alive but a ghoul, you can get the tag from him in several ways- speech, strength, by force, pickpocketing

i had trouble with this myself until i found the house he was in

You should be able to get irradiated dog tags from other areas to outside of camp search light. All it takes is an NCR that is a ghoul, all of them regardless of where have an irradiated dog tag on them.