as far as i know, there is no way to automatically (in a macro for example) open an NPC (a vendor, quest giver or corpse, ..)
So you will need to click it on each of your clones.
There are some mods that allow to pass the same click to quest givers (accept same quests, select same rewards) once the NPC is open. from the top of my head, the addons Multiboxer and ZQB.

regarding loot, you're probably better off having your pary on Free for all, and ppick up everything with your main to distribute later.