1 - The Jedi by way of force in conjunction with saber attacks.
2 - mmm, not quite sure they'd win, but I'd say they have a better chance of beating her then they ever did against Maul.
3 - The Jedi. QGJ is one of the strongest Jedi with the living force and you see what that allowed little Solo to do. Of course, he had Skywalker blood, but ya know. 😉 Plus if OB1 taps the darkside again... why not kill Ventress?