@SaintKadia
Except he did not, as it was explained the frontal assault was diversion for the main, flanking assault. And to be honest, it was the best choice here since he couldn't simply bomb his way in the stronghold. Which is why, kinda paradoxically, it was unsuccessful, because the enemy could predict such move and do his preparations. Moreover, based on the conversation between the leaders, Franz and Celestia, they made their preparations for assasination attempt, which is another good option.
Btw, I'm still suspicious of the nurse. Because, AFAIK, it was not explained how did they manage to get the blood in academy without anyone noticing.
@lastKANAshimi
It's generally disadvantageous to wait out siege, because while you are waiting at the gates, the rest of the world is not. I have played enough strategy games to know that. 😉
Second, it's also bad to let rebelion aflame for any lenght of time since you might be deserted by the opportunists who look to better their fortunes and your political enemies might use it as pretext to depose you. Given the fact that Rezalia's hold of the throne is not as strong as it should be is a considerable factor here.
Yes, the children of her opponents are here, but so are children of her supporters. So any threat to massacre could, and most likely would, be used against her.