Regarding his SP. If he hits two characters who each have two actions tokens, can he distribute 0 dmg to the first character and 4 dmg to the second character, ending up in the two receiving respectively (0+2=) 2 dmg and (4+2) 6 dmg?

Need to quote the power next time.

SECURE AND DESTROY: Sentinel Mark II can use Outwit. When Sentinel Mark II hits an opposing character, increase the damage dealt by +1 for each action token on the hit character.

If both targets have 2 tokens, then yes, you can distribute the damage as you described.