A shy, unconfident brother battles his fear, and uses magic to hide from a villain.
Possible concerns:
Magic. Using magic is a primary theme.
Lack of Courage. The dragon struggles with lack of confidence. This doesn’t really appear to ever be resolved.
Violence. Dragons eat/fight/kill/imprison each other, humans, and beasts.
Oppressive rulers. Wars, treason, tyranny, etc. In this case there is also a mind-controlling tyrant.
Romance. Several dragons have crushes, and romance general dominates this quintet much more than it did for the first quintet.
Darkness. Starting with Book 6, I found the presence of the occult just to be a bit much for me.
Conservatives on the structure of the family may not like that later in the series some characters end up pursuing homosexual relationships. I noticed this mainly in Book 10.