Well yeah Mission is immature but then again I'm sure most of the jedi her age are not much better. As for not being strong enough...well the point of training her would be to make her strong.
Zalbaar would probably be a guardian as you said, but guardians do have
force powers, they just focus on sabers. Although not controlling emotions...well he could be a good dark jedi I suppose
Carth would be good except for the fact that he resents the order for not aiding in the Mandelorian Wars and seems not to like any of the jedi. But he could be trained...given that I had about 3 years to help him get over his trust issues.
As for Canderous...what do you think he would say I you asked him?
Yeah definatly not jedi material.