Sorry for the bold text.
I looked up the set on the wog.ch site and these are the description:
So td;lr the biker gang revived Garmadon as a villain.
On the box art, it shows Zane fighting against one of the biker gang which shows he's still apart of the ninja team:
Another proof is the description:
So pretty much Zane is a spy. Also keep in mine the skin isn't organic since the beginning of the show (i hope).
As for number 3, idk what to say/find. I hope few of they're personality considering the ninjas are sometime irritating at times on the show and TLM personality is still hallow (as in the lack of development) but still easy to point out what motive they have.