"Escape to Salvation" - "Magnificent Retreat" [Campaign 4, Mission 4]

I read your message and decided to experiment – how exactly does it work that "Zephira doesn't let them go underground; a notification appears saying something like, 'I don't want to interfere with the allies.'" Nothing like that happens! If, within a few seconds, while the Wolf, Freya+D, Quijin+G, and Illia cutscenes are playing, you quickly click on the hero's portrait (the one who is fighting, i.e., Freya and Quijin, not Duncan and Gotai), and then quickly press the spacebar and left-click – to "stop" them from running to the Castle, you can calmly enter them, change the artifacts they have from previous missions, take a closer look at Illia, and so on.
Furthermore, specifically regarding the Orcs. K has a normal army to take out the Castle, and G has a ridiculously large number of Cyclops. What do I do? I take the upgraded Cyclops from K and give a small portion, about 1/4, to G. I bring Gotai to the surface (it doesn't really matter, but one should remain below). I send Zephira's troops, give her the Cyclops, and K attacks the Castle. Gotai becomes a blue player on the surface (while I stopped him, he was Zephira's, orange). And I forget about the Orcs.
The key is that Zephira, with these Cyclops – there are about 400 of them – can defeat Biara without allied troops. It's a funny bug; I don't think I've encountered it before.