I finally succeeded by doing just what you said: firing at the turrets. One of my two tanks lost a track and the other one got its gun damaged in the process, but they managed to destroy the weapons of 2 or 3 churchills and knock out their accompanying Cromwell MkVIIIs. Once the guns where useless, my 2 StuG could position themselves to finish off the Crowmwells. All my infantry died during the final ennemy infantry assault on my positions, (except 2 members of a squad) because they could not be supported by my tanks and AT Gun who where ambushing the Churchills and cromwells inside the village. They went out of ammo and where finally submerged. the two soldiers left survived only because my StuGIII who was a bit closer rushed to their help as soon as the Churchills where out of action, helped by one of the tank that still had the hull MG functionning.
One funny devellopment of the battle (of course not so funny at the moment it happened) was that one of the ground attack plane strafing my AT guns was shot down by my Flak38 panzer, and crashed on top of it, putting it out of action, and damaging the turret of my tank hiding nearby.
What bother me is the lack of realism of it all if I want to progress in the campaign: I can win the battle only if I know exactly what the ennemy will be doing and where his forces will move. otherwise, the opposition is so numerous and powerful that it is impossible to survive. I lost 56 infantry, the ennemy a staggering 181 soldiers and about 20 tanks or more, but they keep attacking without ever retreating. Of course on the other end, this is realistic, the germans where unable to withstand the allied onslaught in Normandy, but it gives for a less interesting gameplay, all the more because the missions are scripted in a way that don't let you choose your best troops and armament from your force pool. For example, on the next mission, I don't have access to a single tank (my elite tank crews are no longer part of my force pool), and the several tanks I have in the mission are controlled by the AI and keeps hiding behind the village, not taking part in the battle, being virtually useless. Once the troops in the trenches are out of PanzerSchreck, the battle is one sided, and the infantry is wiped out by the still numerous surviving allied tanks.