If I have a Fig with 2 arrows and Incap with 2 damage and I attack 2 Figs with
Incap + Stunning blow, do the Figs I am attacking both get 2 Damage or do I spelt the damage between the two figs that I am attacking.

You split the damage as you would with an multi-target ranged attack (2 and 0, 1 and 1, or 0 and 2). Stunning Blow doesn't change the way damage is assigned; all it does is add a token on top of what ever damage you would normally deal to your targets.