Anders - has a passing familiarity with firearms, and good hand-eye coordination that translates to pretty good aim with them. I strongly doubt, at this point in his life, that he's going to be comfortable using them against anything with a human face, though. He's also picked up some yo-yo skills that might be able to translate to goofy fighting abilities at some point.

Conner - Largely instinctive proficiency with a saber-like sword and with a fighting staff, as well as with an energy blaster gun. He doesn't have the gun any more though, woe. Regular projectile firearms make him very nervous and he won't handle them if he can help it at all.

Sakura - She's a combat special-ops veteran, so she has a high level of trained proficiency with any kind of modern, standard Earth firearm, grenades, or anything you'd expect of someone with that background. She also has some skill with a sword.

Yitzhak - Um . . . can probably swing a microphone stand pretty well.