First 2 missions in Halo 2 won’t work in Co-op

Me and my buddy we’re trying to play through the whole halo story together and when we got to halo 2 it wouldn’t let us select the first 2 missions

The first two missions being The Heretic and The Armoury? If those are what you mean then those aren’t playable in coop as they are mainly cinematics. In my experience this has always been the way.