You should be able to eliminate the first two bunkers very quickly. When Hellmann and his two armored units have finished the task, order the Engineer that followed them to put a Flame Bunker in the marked location and then send all of them to the Allied Base. Here the Engineer can start a secondary base: a Supply Depot, Research Labs, Tank Factories, and Power Plants. About this time, Hellmann will receive a message that Elsa is to report back to the base…and just a minute or two later learns the message was faked. It sounds as if Aleksei is at work, but the only way Hellmann can find out is to finish the job at hand.
In the north, Preiss and his army can advance east to another bunker and destroy it. Enemy fighters will appear, so you should use the Engineer that erected the first Flame Bunker up here to build a Tank Factory and produce a few Wirbelwinds to ward off the pesky interceptors. Destroy the next bunker (in the northeast corner) and seal off the route, then move south and take out several AT Bunkers and a War Factory before stopping to regroup. You can turn this northeast area into a mini-base, constructing V1 Launch Sites and other buildings; the V1s and eventually V2s can help decimate the area where the next bunker to the south is located so you can safely seal off the fourth of the five reinforcement routes.