Have each player control one squad that acts as a single hivemind. That solves all the balance issues as you could have 3 SM's vs 12 orks, which is close enough.
For alliances, I think there is a Order vs Disorder system in the tabletop game, it goes something like:
Order:
Imperium(There are 3 armies in there), Eldar, Tau.
Disorder:
Orks, Chaos, Dark Eldar, Necrons.
Nid's would be PVE only or Disorder
For alliances, I think there is a Order vs Disorder system in the tabletop game, it goes something like:
Order:
Imperium(There are 3 armies in there), Eldar, Tau.
Disorder:
Orks, Chaos, Dark Eldar, Necrons.
Nid's would be PVE only or Disorder
