Oraxio,
Shooting in cars can be tricky! The only simple fix to your problem is to either use a polarizing filter (properly oriented to comnpensate for the angle of reflection) or perhaps to stage the direction of car travel to minimize the light on the windsheild itself.
Otherwise the solution pecomes exponentially more complicated; namely “roofing” the area from the windscreen forward and using artificial (day)light to illuminate the actors in the front seat. This will necessitate towing the car as the drivers vision will be obstructed by the rig and the lights in his/her eyes. Power for the lighting can be carried in the tow vehicle, either 120 batteries/invertor or a generator.
Another alternative is to “process” the shot by shooting on a stage or other controlled area, with a blue or green screen in the backround, shooting plates to composit into the screened area and recreating the daylight lighting quality on the car and the actors.
Hope this helps!
JS