I'm not sure if this has been suggested or not. If it has not been suggested, then here is a suggestion. I think there should be /trust, you know. Like in skyblock.net. /trust (player) allows the other player to build, open chests, etc on your island.
There's /island invite [player], but I guess /trust is relatively more simple to type. I just don't really like the idea of becoming so similar to skyblock, though. Edit: Support.
A updated version of uSkyBlock (the Skyblock plugin for mv Skyblock) has the command /is trust. They could always update.