"The Will of Ashan" - "Heart of Darkness" [2nd campaign, 5th mission]

Help! I've already sacrificed all the Necromancers at the altars, but I can't find the passage to the Assassins. I went to Sanctuary, and all my monsters are undead and upgraded, but I still can't defeat this demonic army, and they have a strong catapult. Could it be because I didn't fulfill the ghost's request?

Added after 13 hours 32 minutes
Help!

Dear FRIEND... You don't even need to fulfill the ghost's request... But if you do, you'll get one of three bonuses... The best one is the hero Valeria, or somewhere else, they'll give you a lot of zombies and mummies... Gather a bigger army and go to Sanctuary... And the ballista can be taken down with 1-2 liches... Also, level up the "Banish" spell and the "Horror Scream" ability... The mentor will help you with this... You can find him in the western part of the map...
Good luck... Tear Orlando to shreds...:smile34: