Walkthroughs for custom maps.

If you have a Berserk, you can use other heroes with fire magic to attack Madre, weakening her with hit-and-run tactics, since the city is nearby, and Madre is ordered to stay put. And when there are significantly fewer dragons left, Baltazar will be able to defeat Madre in battle.
This situation shows that bad luck with something that drops randomly can have a fatal impact on the Walkthrough.
I looked again: unfortunately, someone has already dug up the Grail! So, either accept it, or start over.

No one could have dug up the Grail. Below that location, there was a stationary hero, whose death triggered the guardians, and there was no Grail with him. The portal itself was also guarded, for which another hero was killed, and so on. The last portal led to Madre's land.

Therefore, 2 Grails on the map are not possible. I'll try hit-and-run tactics with other heroes, but it's unlikely to work. It's a pity to waste time, but never mind, I'll replay it.

P.S. Someone in the link above got a Berserk, and the Walkthrough is practically the same for everyone. Maybe I missed something, I'll check every inch of the map.