Anyway, I made a revision of Strongpoint's plan.
1) Use our demonic strength to maintain fear in their minds. Encourage betrayal
2) If we can do it with only minor investment of our power and from the safe distance > raise their fallen comrades as zombies. Not for real impact effectiveness but to force them to kill their own friends
3) Our undead horde should stop hiding. In fact, they should do the exact opposite. Malkus must find a way to make it look like we have way more than few hundreds of undead.
The undead will be placed in such way that it looks as if they can storm the fortress at any moment;4) Mkilizk, Brutewolves and Wolfmaster should fill the air with howling. Again, enemy must be sure that they face way more than few wolves. Also, they should participate in the sheep plan
See sheep plan5) Imps, spectres, traitors should do small scale harassment attacks retreating at any real resistance. Setting things on fire, damaging\destroying bridges, killing lone soldiers, scaring sheep and other livestock, doing various acts of sabotage. It is totally fine if we lose some spectres or imps. Discovered traitors don't bother us either because if they will be captured this will create a sweet distrust among their forces.
Take the opportunity to loot the warehouses, they may contain usefull stuff for our forces and are probably not well guarded6) Rock trolls should keep throwing rocks from from afar.
Target priorities will be the skybridges, seperating the main compound from the rest of the fortress7) Should the enemy try to break through and attack our undead horde let Malkus lead the army and enter the combat after roughly half of our zombies and skeletons are destroyed.
In person, reuse the worm form to execute a series of smash and grab attacks. Smash the underground spring (check first if it isn't holy or something), grab the enemy leadership, collapse their ways out of the compound, consume the sleeping rooms, that kind of stuff. Emphasis on smash and grab, don't get bogged down. We want the enemy to feel fear if they see us retreat, because that means they no longer know where we are and we could strike at any moment.
With much outlying village destroyed in the siege, and the shepherds hiding in the main compound, it's likely that the sheep flocks and dogs are relatively unguarded. Besides, logically most of the flock would be rather far away from the compound at any point in time, because they need to graze to eat and any decent size flock would consume everything near the city in short time.
Using spectres to scare the flocks away from the village, and the Wolfmaster to incentivize the Dog's natural instinct to herd the flocks, it should be possible to push them into a place away from the shepherd where they can be fully taken over by the Wolfmaster. Any particularly stubborn shepherd can be dealt with by the Brutewolves.
We can then slaughter most of the sheep as a huge offering, replacing quality of the sacrifice with quantity. Whatever trickle of evil comes from that should be used to enhance the hunting dogs. The rest can be lit on fire and made to rampage into the city.
The argument for intervening ourselves remains very strong. See, our previous attack worked perfectly well, killing many civilians, until we got bogged down trying to kill everyone. The enemy needed to dedicate 2 dozen archers, many priests and soldiers to drive us of. I'm generously assuming that was about 50-60 men. And they just don't have those forces. They only have 141 soldiers+ priests, and since they have to guard day and night, that means they'll have to split them up. So, they'll only have maybe half of that on patrol most of the time. Still a respectable amount but they have so much to guard. They'll need to post 40-50 men on the walls, to prepare against a potential attack, and then they'll only have 20 left.
Edit : I just found out that those little random star things are abbreviations.