Ranger – “Defense” [Campaign 5, Mission 3]

I'm new to the game, but can you explain how you manage to save your dragons when Fardane captures the capital at the beginning? If I try to protect the dragons, almost nothing is left of the army, and I especially regret losing the archers and druids. If I send them into the attack, the dragons are killed, but the army remains more or less intact, but I can't split it to send another hero to the other side. Then I can't hold the capital. As a result, I have to stay in the capital and build up my army.

And again, there's a problem with completing the mission (I played with cheats, killed everyone and freed them, but the mission doesn't end). I want to play it fairly, otherwise my conscience bothers me.