Firstly, do your boats have bilge keels, they might help with the roll. Secondly, A weighted keel under the hull might help, similar to what yachts have, you would have to experiment as to the weight and depth of keel, you don't want to make the boats to stiff though as all boats lean and roll.
I had a problem like this with a model and one of the issues was that it was single shaft and I had too much torque from the motor and on take up it would lean alarmingly, the weighted keel did help, but the truth was I had too powerful a motor for the model, hay ho!