I played through this mission, and here's how I did it, as it was the easiest.
First, I gave all of Duncan's troops to Wolfenstein and left Duncan himself in the city to build up an army, just in case the enemy attacks. With Wolfenstein, I started by searching for all the obelisks, which took a couple of weeks. I built the Tower of Ashera in the city. Meanwhile, I went to conquer the mines and gain as much experience as possible.
After a few weeks, Lorenzo attacked, but Duncan repelled him.
Then, Laszlo arrived with much larger forces. Soon after, Wolfenstein arrived and defeated him. After the victory, I gathered troops and stormed Horncrest, and then the city next to Horncrest.