Kinda find it funny how Brand. The guy who wanted to Free the eggs from Quetz oppression. Is fine if they all burn to death. Like say what you want about the Guards. The town folk do not deserve to have their town burnt down.
This isn't even taking into consideration. That the Aves are not even a threat. Like their bound to run out of crossbow bolts eventually. And then what?
IMHO he did it to spite the Quetz, not because he particularly cared about the Aves. He enjoyed bullying them into committing high treason, or so he thought.
As for the villagers, who birdboxed Laputa in the first place? They did. And that makes them enemy support at this point, not innocent civilians. As I said, this is an enemy village now in Brand's thinking and
he isn't wrong. Saida is so used to thinking of the Aves as part of her family, she forgets that their one and
only loyalty is to Vetra-jou. She better get with the program quick, or she isn't going to be able to protect Brand for long.
Finally, Laputa certainly will have a ton of arrows for their Aves. If I were Relshen I'd make sure to have a supply chain ready to go, so they will
never run out. And once they realize Dragon!Saida is a meat shield, they're going to flank them. Even a birdbrain like Relshen probably knows that many tactics. And so does Brand. The flames will prevent them from cleanly flanking their position, and trap them in a vice. Do they want to 1) Face a volcano dragon and an extremely angry quetz, 2) Burn alive, or 3) Retreat as fast as they can from that house.
Let them worry about putting the fire out. It gives Brand and Saida a clear shot out of there.