I have recently installed 'The Pitt' and 'Operation - Anchorage' add-ons, now during my wandering in D.C., I keep meeting four characters in power armour just along from the Jefferson Memorial. They comprise two humans, a ghoul, and a super mutant, all are friendly but do not respond to questions. Even wierder during the final battle in D.C. they just apear to stand there and let themselves be killed. Are they from the above add-on or are they from one of the other 'mods' I have installed and how do I interact with them?

I think they are from one of ur mods, because I've never heard of any npcs like that in The pitt and Operation Anchorage.

Perhaps it's another Lone Wanderer with his party of Foggs the Super Mutant, Sharen the Ghoul, and Jerryco the Ex-Raider? It's fun to think of it that way. That's a good idea for a mod: make another party of adventurers out in the Wastes that does stuff like the player.

I think it's one of the random special encounters. Is there a fridge nearby? (Or was it a barrel?) Anyway, there's an encounter where four NPCs are arguing about water or something.

Before I even find dad in Vault 112, there's this power armored Enclave soldier hanging around near Dukov's place -it's the road that leads away from the river, opposite the Anchorage Memorial. He keeps respawning and is extremely hostile, Is he supposed to be there, this early in the game?

I would say the Mutant is Uncle Leo as he is the only friendly super mutant you can meet in a random encounter. Anyway, do the other character you have mentioned have names?