The way I interpret Bounding Fire is you can move multiple units together and they will make a bounding fire attempt together (assuming they moved to the same space) as a single firegroup. The alternate interpretation is each individual unit will make an attempt on its own, which seems counter-intuitive, but could be the actual deal. Which is correct?
You can bounding fire units that move together as a single firegroup.
The question here is, does that one PMC counterattack against just the MCU that fired at it, or against all units in that space where the MCU landed?
All units in the space.