Oh and who are "the three"? I don't have gold anymore, if you were suggesting you, John, and I.
Anyways, the Forerunners didn't really fuck us up. We were on the sidelines, so I suppose if any of the characters did meet it would have been during a time of peace. Maybe during training (not war games, unless that tech was developed before Infinity in this timeline) but that's the closest it'll get to a war time bond.
As for Manuel, I suppose he'd be an acquaintance at most since he was mostly a lone wolf during his time with ONI. When Walter gains control, and offers Manuel a position of power I suppose he'd take it. Then we'd see Manuel's process from "light" to "dark" AGAIN. Sounds bad to do it again, I know, but it makes the most sense.
Argonous would probably be a friend of Manuel, but have his hands tied up dealing with Forerunner oppression on Doisac.
What about your (as in the rest of you) characters?