I am currently playing with people in the same town, and (if I'm right) there is currently no way to have a container that is still protected to have 2 or more players to be able to access it. It would be really helpful if this was added to improve the multiplayer experience.
you can already add people to access chests by using /cmodify {username} then click on the container
You can also use /cpassword to set a password to open but thats annoying
There is also /unlock to open the chest for everyone, then it only open for people in the town i believe