Yes, you can use any game engine you want! Team members can join the jam, but it's optional since everyone will be allowed to vote. I recommend to join just in case that this rule have to change.
Thanks.I got another question. I'm just starting on Godot so I'm still new at it and i will be using this GameJam as a excellent excuse to push myself to learn more. Q. Is there a NO "bad" games/Unfinished allowed rule?