You've already got Mutiverse, so you might as well add some add-ons on that improve it, like this one.
Allows you to manage inventory related things when it comes to your worlds, such as world specific inventories, etc.
Spigot: https://www.spigotmc.org/resources/multiverse-inventories-for-1-9-1-10-1-11-1-12.21681/
Bukkit: https://dev.bukkit.org/projects/multiverse-inventories