5th cave is piece of cake if you chose all shooting units (Witch, mermaid, Kentaur etc) and chose freeze trap, lightning bolt, meteor and comet spells. The bombers cannot touch you, and you can mass destruct them with the spells. Have luck!
Kinght6 - have some (4) catapult with ability of fast move (dunno what's the name). Quickly eliminate the attacking forces. Do not go out to the open field, or you will be slain by the archers! Use the catapults to kill the shooter enemies, while attack on the mountains where they cannot shoot at you. Some strong dwarf and/or the dwarf hero could be handy on this map. Have luck!