You're a wonderful guy, Origami, with a lot to live for. This talk of splitting your brain is alarming and utterly premature. Hopefully you'll reconsider?
Anyway, I'll be travelling for a good part of this week, so I'm going to speculate on tactics a bit further on.
This turn, Percival and Denton should be on the move toward Curbiston. Meanwhile we are negotiating with BK. Say then that we get BK on our side, we meet up at Curbiston, and rush down to crush the new raider settlement before it is properly established and defended. The Duke can't leave before he feels safe on the homefront. Hopefully Count Zanders and Gorgan also converge on Torchester.
Here's the more uncertain part. Fallsberg is near a large waterfall, so I assume that it's inland on the main river. The raider settlement is basically the coastal supply point. While the Duke oversees the gathering of a relief forces, we enter the region between Fallsberg and RS. The raiders probably have a great deal of supplies being carted up that corridor. We harrass them for a bit and, perhaps, recapture one or more of the strongpoints between Fallsberg and RS. The raiders have to peel away enough troops to engage us and re-establish their supply, but not enough to allow their siege lines to grow porous. It's a balancing act for them, and the result weakens them at the siege and in chasing us.
Finally, the Duke will arrive, and we take the RS from them. They will have to fight us somewhere between Fallsberg and the sea on a ground of our choosing. Otherwise, they are cut off. Unless the circumstances change, we don't want to ever fight a battle at Fallsberg, where the King has only a small and beleaguered force to join us and the enemy is undividedly strong. It's better to use their siege to split up their forces.