You would have to ask them. Every Guild is a separate entity, with the leaders making rules. what the require to take part? you would have to ask them.
I would say things like taking part in GvG, taking leadership roles in GbG, finishing GE 64 quickly, maybe having to have a Arc to do 1.92 or more yourself. there will be strings. I would guess joining and doing very little is never going to get you into getting 2.0 in your GBs. Also you can go look at the Guild, check who has what level Arc. Usually 2.0 is only for P1, and maybe for P2 if a second person has an Arc level 180 for only some Great Buildings that the Guild is wanting leveled up. Stuff like Observatory would be one such. Arc too.
A 2.0 offer is rare. not many players can offer it, and of those that could, few do. So a 2.0 is even rarer than having a level 180 Arc.