Letos and his general plague tired me out a bit. I fought him a couple of times – it was tough, although I probably didn't have the best build for Railag.
As for the paths to the Castles, look above; there's an open map there...

Using an open map isn't interesting. It's the same as using cheat codes, which I don't know and don't want to know. However, the other day, a friend who I was playing HotS with showed me how to cast 2 spells per turn without using cheat codes (S+A). I don't use that either.

I've already found the third Castle. At the gate, there's a hero with one Assassin. I think there's someone else inside. Most likely, it's Letos, who fled from the battlefield. It's a shame that Railag has a relatively small army. There isn't a single dragon. However, all 6 types of units are upgraded. May the heavens help him and generously shower the enemy with enhanced meteor showers.

After buying Kifrah, level 14, in the second or third week, I regretted buying Vaishan, level 1, in the first week. Now I don't regret it, because there haven't been any hero-warlocks in the tavern for a long time – only rangers and Knights.

Added after 3 hours 39 minutes
As soon as I complained about the lack of the right heroes in the tavern, Irbeth, level 17, showed up. I appointed her as the commander of the third city, which was taken with the greatest losses in this mission. Railag had to stay there until the end of the week to replenish the army. And at that time, a level 18 hero was roaming around. He captured an outpost of the Order Castle, took angels there, and went to the second city. Kifrah, level 14, was stationed there with a decent army (Shadia is stationed in the first city with an even more decent army). He didn't dare to attack. He hovered near the city until Railag returned.