Quick turn resolution question - Storming Castle

[moderation]

I'm about to storm a castle that I'm fairly confident I will conquer. I am expecting an attack from the enemy on the same turn and I am also sending some mages to reinforce my besieging army on the same turn.

So if I conquer the fortress, I'm wondering if my units will hide inside when the enemies attack or if they will fight outside. In addition, I'm wondering what will happen to my mage reinforcements. Assuming I conquer the fortress will the mages:

a) Join the troops inside the castle?
b) Fight outside on the field with them?
c) Something else entirely?

Also, I would actually prefer to fight enemies attacking from outside and storm the castle on the same turn rather than have to waste time storming the castle and then fending off their puny attack. Is there any way to do both things on the same turn?