For fighting Berserker at Swinebrook, use Guardsman first, Skirmisher for 2nd, and Helian Archer for the 3rd. Usually only the Guardsman that died, and the other 2 can kill the Berserker.
and for killing the Son of Khargat at Brinewood use Scout for 1st and Border Cavalry for the 3rd, since the enemy deal extra damage on infantry unit
Easy win with scout only, for mid and late stage. just spam scout on 1 line, ignore any hard enemy, spam until their base camp become zero, then use engineer morale wave (since it gonna full) to recover your base hp, then finish the remaining enemy army (usually only enemy archer left)
and the main team is 1.Spy for rescuing 2.Heli-R for picking up star that Spy can't reach 3. Commando for sniping 4.Artillery for Finishing 5.any unit you want...
tips for rescue stage: 1.buy Spy, rank up to the max 2.Buy medic kit 3-5 3.save civilian and VIP by rushing at enemies first (look out if the enemy on right side of civilian/VIP, since it will shot to your directly, and beware with Heli-R since can 1 hit kill the spy) 4.Evacuate after finish pick all up 5.and Finally... Boooom Baby!!