With EssentialsSpawn, would it be possible to force players to spawn on join if they are logging on in specified worlds? For example, if someone is in an arena world, force them back to spawn on rejoin. If someone is in a normal survival world, don't force them back to spawn - they login back where they last logged off.

Simply use the group option for spawn-on-join and remove them from the group on the excluded worlds.

What if I don't want them to inherit that group's permissions?

What I would like to do is have it so spawn-on-join forces my Guest group to spawn every time they login with spawn-on-join: Guest and if anyone logs into the world void (which I use for arenas), force them back to spawn so they don't relog in a world they aren't suppose to be in unnaturally. Having a world exclusion list to force spawn regardless of grouping seems much more fluid.

You can use LuckPerms and create groups that don't have any permissions.

I agree that this is a useful request though - I don't think even LuckPerms lets you control parent groups by world.

LuckPerms allows for this nowadays, closing.