How many men does Bjan have. If he brings the sort of force that Harbaal could easily put in the field - not a major army, just a large expeditionary/raiding force of 1000 huscarles and 2000 volunteers/clansmen - then Bjan will have troops to spare. He can quite literally take on all three fortresses at once. Leave 300 or so men at each of the keeps to bottle them up and eventually take them (say 50 huscarles on foot, 50 light horse, and 200 volunteers). With the rest of the force he moves on south, takes Olokand by assault, and then garrisoning it with a force of about 400, strikes south into central Kaldor.
This is a lot of troops. I'm assuming a 60' warboat can carry around 60 troops and an 80' 140. This is stripping the ships to a minimum of stores, and assuming that each man carries his own provisions. 3000 troops would require some 22 of the latter. This is including no horses. Anything larger and I'd begin to wonder about draft. I could be overestimating this issue, of course.
However, I agree that it would be tactically sound to attack all three to prevent their coordination.
The raid into central Kaldor comprises approximately 2000 men. To match this (with combat effectives, not levy) will require a full feudal muster for the kingdom. Provided Bjan keeps moving and doesn't give Kaldor time to concentrate, I'm not sure there is anything that can be done to stop him.
If Bjan loots and burns/destroys Baseta and Setrew, then he only has to garrison Olokand (he will want something to fall back upon if need be). Allowing for casualties, this means a force of around 1500 for the raid. They will probably be able to loot horses rather than bring them along from Lorkin.
My general thought is the raid would travel in a large circle from Olokand through heru, Tashal, Querina, Kiban, Shebra, Fisen, Uldien, Getha, insert grab Silver Caravan here
, Gardiren, Yeged, and back to Olokand. It could also reverse and go the other direction. It's probable that few if any of these major settlements would be captured, but the surrounding manors would be sacked and certainly those settlements lacking walls would be. Such a raid would no doubt take several months, living off the land, getting a bit slower as plunder accumulates. Once back in Olokand, the force regroups, and heads for the boats.
I see this going really badly for Kaldor. Assuming the Harbaalers show up and start knocking over keeps, they might be over Olokand's walls before Tashal knows anything is happening. Depending on how long Olokand takes and some dumb luck, Tashal might not know that anything is wrong until a flotilla of boats appears on the riverfront.
This is my plan if only for dramatic reasons. Maybe not boats, but certainly an army. Someone will no doubt manage to get through to warn, but I suspect the city will be able to do little but lock the gates.
I think what will be key to the Harbaaler campaign/extended raid is what they do after Olokand. Clearly to maintain their momentum and keep Kaldor rocking back on its heels they need to continue their attacks. Assuming they've reconnoitered and know the local map, as it were, I imagine Gardiren, Tonot, Yeged and Bidow are the target of the main force, with a smaller force sent to create havoc and burn stuff in Kaldor's heartland.
This is certainly another option as opposed to my notion of keeping them together.
Probably the best strategy from Kaldor's perspective is to fully garrison every fortification and then assemble the largest mounted force possible to shadow and harrass him. Chelni or Hodiri mercenaries en-mass would be very useful for Kaldor here (and also useful for Bjan if he can get them).
I hadn't thought about involving the tribes. Interesting idea. One wonders what their price would be - steep, I imagine.
Time for a daring bunch of PCs to raid Fana and get hold of the Horn of Kergis for the King.
Heh. My PCs would be more likely to retrieve the Sword of Calsten from where they stashed it and bring down the King of Kaldor.
What about the Khuzdul? Do you think they will trade a nice cosy relationship with Kaldor for some unknown relationship with a bunch of Hairy Harbaalers?
Highly unlikely. If I were the King of Kaldor I would be sending an embassy to the Khuzan post haste to ask for their help. Especially if the Silver Caravan is seized.