There are macros available, and even a quest mod made for multiboxers, to accept/hand in quests on main and slaves at the same time.
However you still have to select/talk to the quest NPC on each character.
Looting has to be done per character as well, as 99% of the time quest item drops are soulbound (they may not say it).

For quests that need an item you will need to accept them all manually, however any quest which is sharable can be accepted via a /script on the slaves. Have a look in the stickies for the macro.