Don't turn into a dragon and he will not summon the flying creatures. Just use your standard boss battle procedures (summon your creature, etc, maybe take a few stat and armour boost potions before getting close enough to trigger the initial conversation, etc). You can also clear other areas in the fortress, or move on to others, and return for him when you are at a higher level, or have better equipment, etc.
EDIT: 24 seconds late...
lol. figured that out. But I took dragon for anyway and killed the two demons. Then just ended up having to fight him normally because breathing fire on him did about 6 damage. Right.....
