"*Does this add-on allow your second character (slave) to actually copy the acceptation of quest my main does?
- For example: If I go to an npc with my main, my slave will follow me (cause of /follow macro). Then I will talk to the npc and select a quest. Will my slave automaticly
talk to this npc too and accept the quest? Or do I need to use the share quest option, and then accept it on my slave?"

No, you first must open the NPC window on both. Then it depends on the quest, but JAMBA does all it can to help. (you can't share quests when the NPC give you an object)

"*Does this add-on allow you to perform the actions needed for an quest on your slave (mirrored from my main)?
-For example: I accepted a quest on both my main and slave, and now I need to plant a banner. If I plant this banner on my main, will my slave automaticlly perform this action as well?
Or how do I need to manage this?
"

Depends on the quest. Some will give credit to every party member ( the good quests, MB wise) and some won't. Jamba can't help here

"*Does this add-on allow your character to automaticly repair stuff at an npc?
- For example: I am talking to an npc with my main. I select repair all items. Will my slave automaticly repair his items as well?"

Again you have to open the NPC window. Jamba has a option to auto-repair.