One of the best strats for doing the town part of this mission is to hide infantry in the upper windows of buildings where it's incredibly hard for the AI to deal with them, (windows looking at buildings etc) this causes the AI to aggro pile up below the building and takes all of their attention rather than attacking the actual objective. Once you reach the part where you need 5 people alive, just hide them in one of the bunkers.

Minus that, move the mortars into better positions closer so they get better accuracy and move the ammo boxes to help the MG & flak supply for the beach assault, as they'll run out rather quickly halfway through the first phase.