Awesome, and I love the concept of the paired PrC. It's well put together, quite straightforward, but I'd say a little underpowered. I suggest putting together some interesting additional power somewhere, something in a similar tune with Improved Flanking: being more effective when working as a pair.

Perhaps, a double attack ability where they may both attack the same target and both use the higher of the two attack rolls, or perhaps allowing some kind of co-feint that gives one a huge bonus to hit if the other takes a feint-esque action.