Quick questions:
 

If you're under siege and summon, do the summoned creatures appear inside the castle, or in the province where they initiate a battle with the besiegers?

Can you attempt a limited breakout? Set part of your defending army to breakout, let them fight a battle, but the other half stays in the fortress?

On the same lines, if you attack a province where you are under siege, does the garrison automatically try to break out and join the battle? It's just I once tried to raise a siege unsure I'd win, and despite - as I recall - not giving the garrison break siege orders, I think they joined the battle. But I might have remembered my order wrongly.

Re: Quick questions:
 

1) Inside castle, unless they are special monsters like Ghost Riders, which you do not get to keep

2) Yes. Only the troops with the commanders woith break siege orders will participate

3) You remember incorrectly. You must give break siege orders for them to join forces with the outside rescue.

Re: Quick questions:
 

Many thanks.