Long as the founding GM of the campaign is a mentor, all players/co-GMs can use the results of the API scripts the GM/co-GM has installed. None of the others need to have mentor to take advantage of them. And a co-GM can do most everything a GM can, can see the tabletop the same, add/remove tokens, characters, handouts, music, rollable tables, and so on like a normal GM. Only options they are locked out of is campaign settings like name, character sheet selection and such. But they can install and update the API scripts window also even if they aren't a mentor (assuming the GM that created the campaign is one).