Having looked into the castle, via google map's street view - that is one nasty looking fortification. I can see why you chose it, even by modern standards it's well situated. It's surrounded by loads of dense streets too, which will stop the Russians from swarming on it. Then you have the almost vertical climb of the hill itself, making the causeway the only plausible way of a direct assault. A tactician's nightmare.
I'm going to enjoy working out ways to take this thing.
So we've got five bad asses with 5 bad ass fire teams. High walls. Steep climb. Solid structure.
*goes to research Russian climbing equipment*