Nat/Clint/Morgan/Nebula
That's the main thing the attendants do. The groom has groomsmen who do the same thing. Yes, it's a way of supporting them. And usually there is a dress involved. That's up to the bride, she figures out what colors she wants and that's what you wear.
And yes, I'm sure you won't have to kill anyone. That would make for an interesting reception though.