Every bro might nad hidden perk which can be revealed through some battles or time.
Small sweet advantages or disadvantages.
By the way, 5% chance for every bro to act his turn out of player control is very nice idea.
It might depend on backgrounds (more on wildman/raider/noncombatants, standart on most other, negated on old soldier/swodmaster and so on), also depends on irrational/disloyal/dastard/cocky/weasel traits, negated by loyal/determined/whatever else.
White flags can increase that chance too.
Also it might depends somehow on current bro, offensive or defensive he would behave.