Instrumental parentification is a feature of many dragon families. It is normal for the older siblings to care for the younger ones. Usually the size difference between parents and their offspring justifies it to an extent; adult dragons are enormous. Mundane things like bathing the newly hatched and restraining unruly tweens can be downright dangerous if the parent tries to do it.
However, there are times it gets taken too far.

Garble was somewhat neglected after Caldera stopped worrying about his safety 24/7. She didn’t want to smother her son with too much care, but in her attempt to reign herself in she ended up taking it to the other extreme. Meanwhile, Maximus had no idea how to raise anything except an army, so he focused on providing for the family and giving Garble a robust physical education.
At a young age Garble learned that if he needed something, the only reliable way to obtain it was by getting it himself. Being as physically fit as he was, this usually wasn’t a problem. He was starved for validation, though. His mother’s mordant sense of humor didn’t help matters.

When Smolder hatched, Caldera was initially worried that Garble would be very jealous of his little sister. But the young drake adored her. Garble was old enough to understand why a hatchling needs more attention, and why his help was enlisted sometimes. He loved the idea of having a playmate in her as she grew older. The responsibility of caring for her made him feel significant as well.
As Smolder grew into a mobile baby dragon who could walk and talk, she became glued to her big brother. Garble was her hero and she wanted to be included no matter what he did. Though there were times Garble craved privacy, he reveled in the attention for the most part.

Caldera was elated that her babies got along so well and didn’t realize that she was becoming gradually more critical and demanding of her son. Not only did she come to rely on Garble’s help raising her daughter, she began holding him accountable for her mistakes. Since Smolder tried mirroring everything Garble did, she’d punish him severely for messing up, arguing that every mistake he made in front of Smolder was a mistake he made twice. She also scolded him for wanting to be Smolder’s hero, calling him selfish for leaning on her dependence on him — something that she had chastised herself for when Garble was much younger.
This all made sense to young Garble, so he internalized that guilt. On top of this, he had his stoic, high-ranking father’s footprints to fill.

Garble grew hyper aware of his perceived shortcomings over time, compensating for them by putting forth the image of being a “dragon among dragons”. Another way he compensated for them was by taking his responsibility as the oldest sibling very seriously. He wants the best for his little sisters and sometimes that means being a bit tougher on them than he’d like…

That said, Smolder really pushed his buttons this time. Climbing all over him and tugging at his wings for attention is something he can ignore, but she can’t push her head against his chin. Those horns of hers could poke his eyes out!