Yes, you can. You can press /f unclaim. This will unclaim the land that you're standing on. (Basically, the opposite of /f claim) You can also type /f unclaimall, which will unclaim ALL of your factions land.
Chat with our AI personalities
/f unclaim
There are no co-leaders in factions because there can only be ONE admin in a faction, but you can make others mods by pressing /f mod usernamehere. Mods (or moderators) can kick other players that aren't mods, change titles of others, claim land, unclaim land, etc.. They have a lot of functions, but not as many as the Admin.
You type in the command in chat /t unclaim while standing in the plot.
To answer a faction invite just do /f join <faction name>
You use /f leave [faction name]