do these talents stack?

What do you mean?
You can't activate them both at the same time (one is used when you attack, and the other - when you are attacked).
If you're asking whether the 'timer' for Disorient starts ticking after the enemy is no longer staggered, or when they have just been staggered, the answer appears to be the latter.

As above disorient helps with overbalance disorient causes someone to get disoriented so will add stback onto the check for a number of rounds equal to it's value, it doesnt stack with itself, if you hit someone who is disoriented then it adds to the duration. Overbalance staggers your opponent (they lose their action next round essentially), and because its triggered off setback, when your opponent attacks you wqnt as many red dice and black dce in thier ceck as you can.