I will answer the second question first. Yes, you can have multiple GM's in one game. The game's creator can upgrade a player to co-GM status very easily. Keep in mind that Co-GMs can't do everything the Creator of a game can. From the Roll20 Wiki: Promote to GM will grant that Player GM status in the Game, commonly called a co-GM . This is useful for jointly running a Game with someone else or if the Creator would like to become a Player in a Game they created. Promoting someone to GM may also be beneficial in helping another user with GM-level features and or solving Game issues. Promoted to GMs , have limited control over a Game : Cannot: Change the next game time display. Change the Game's description. Change the Game's settings options, such as the version of Character Sheet that is set, toggling public access, changing the background image, toggling character import, or list the game in Looking for Players. Delete the entire game. Kick or Remove Players . Clear the Chat Archive. A Co-GM will not have access to the original Game‘s Creator‘s image library, character journals, handouts, decks, rollable tables, and other games' pages, however those elements that are being used within the game are available to the Co-GM. Images that are being used within the games' pages can be manipulated by the Co-GM as long as they remain within the game editor. If the Co-GM removes any of these shared elements they will not be available unless the Game‘s Creator restores them to play. Can: Full access to all layers. Create a new map page. Put pictures and tokens to the tabletop from their image library. Assign and edit tokens. Add handouts, new characters, assign journals. Move the Players ribbon to different maps. Play music from the jukebox. Read GM whispers. Make macros and token actions and show or hide them from players. Control dynamic lighting settings if the Game‘s Creator is a Pro or Plus subscriber. Now to answer the first question. It really depends on how you are going to run the game. If you are going to be running voice games, it takes two or more people in the room for the webRTC to be active. If you are talking about play by post or asynchronous text style games then yes, it is very easy to do in roll20. Players are not restricted or denied access to the game when the GM is not there so they can come and go as they want. If you have specific questions about how to do those games in roll20, please feel free to ask them. I've been running text based games here on roll20 for years.
