Hey, I think some rebel settlements should be very hard to take, like in the books. Due to engine limitations, some strongholds are much less formidable than in the books. That should be compensated with soldiers. The Twins should have a lot more soldiers garrisoned, and not just 200. The Freys were powerful and numerous, and the lord's family alone was close to a hundred.
This way the Twins won't give in to anybody, but rather the first large army to arrive. Just my two cents.