Are you stuck again?
Describe the hero and how many units you can gather in the army, and I'll think about how to complete it. There's always a solution.
No, I don't kill everyone along the way because you can lose a lot of units, especially the ones you need. Or, if I know who they are, I can easily defeat them without losses. Try lowering the difficulty level for this mission. I only return when I'm nearby, for example, on a ship. You can return to the island with units in 3 days, but you have to do it towards the end of the week so you don't have to run back and forth many times.