if you are playing the x-box version, my advice would be start with a demolition spec, move up the road on the left side of the tanks, use the map to postion your computer controled team up too where the first enemy tank is positioned. When you get to this point which should be before anyone else including the tanks, take out the enemy tank, and the two dummy's. Move up the road take out the guy around the first corner with the RPG, and clear the university defenders, then move the team you are controling back to where the first enemy tank was, the three tanks you are escorting should remain still, because you haven't advanced. Then take out the defenders and the two tanks at the second objective, at this point the tanks you are escorting should start moving, by the time you have cleared the second objective they will be arriving.
or you could just save it as you go along and you'll eventually do it