Seems pretty easy. Got max jewels at third map. All others are in legendary and axe is Earthbreaker +2 already.
Seems to me the next maps would be a breeze so...
Adding grenades to your units is a must. If you are having a hard time dealing with the mortar guy or snipers, make sure you have "Air Raid" or whatever that airplane skill is, and use it to kill the snipers and mortars. It's not accurate though, so don't count on it too much. And most of the time, combination of tank and assault team will do the trick. Mortar guys are also very helpful when there's too many infantry guys hiding.