1. Arcann is inferior, but can contend with Luke; with Vailyn's raw power and two others, they win this 7-8/10.
2. This could potentially go either way. Arcann can give Luke a good fight on his own, but in a fight of this caliber, with Luke's absurdly high speed and stuff, can the others provide enough aid? Dunno.
3. Well, probably team slightly. It's combative toss-up, and advantage in the Force as a group, but it's also nearly impossible for the team to gather their collective strength and overpower Luke in an incredibly heated fight; a fight that, again, can go either way though.