You need 2 keys setup.

1. Assist - bind to an assist macro on your alts that assist your main
2. Interact - go into keybindings and set a key for Interact with target

Once this is setup you just need to select a quest giver or corpse or flight master or banker or whatever on your main, hit the Assist key and then hit the Interact key. If you select a quest giver, assist and interact then all your characters will talk to the quest giver and then Jamba will mirror the selection for you.

You need 2 keys as I don't think you can macro the Interact ability.