Hi, I need at least two others to help with the achievements:
- There's no "I" in "Team" - complete 15 missions in co-op
- United We Stand - complete a boss in co-op
- And They'll Tell Two Friends - Play with at least two other players

Probably makes sense to start a new campaign with two other people, do the 15 missions and go do a boss after if not already done. Add me or comment below if you're interested.