I just completed the 2nd to last battle, it was brutal but I managed to beat it by ordering my people to retreat and aggressive turn to turn to prevent them from charging ahead of me.
I soaked up LOTs of damage, and used a insane amount of stimpacks but everyone survived including my rescued slave who did her job and drew a little fire.
I had to reload once because I armed allies with grenades, that was a HUGE mistake, talk about friendly fire! Restarted the battle and took their grenades away and stood up front drawing fire and shooting with a few shots, healing, and rearming my grenades when I could get them off.
I had to take out the heavy gunner enemy FAST. He was burst firing and doing damage to his friendlies, but he also threw grenades which was hurtling my team BAD!