Email the airline to get a definitive answer on your specific items.

Small music instrument seems less vague when put next to the violin & guitar examples and the requirements of being in a case that fits under the seat or in the overhead bin. Instruments such as a cello or a standard sized keyboard do not qualify as they do not fit the requirements and space requiring one to purchase its own seat for the instrument. A Theremin would be considered an instrument but would have to satisfy the other requirements.

Delicate and fragile have to satisfy the carryon policies. You can't bring a standard checked baggage bag on the plane just because you're traveling with fragile goods. For example; No wine bottles that are not purchased within the secure area as it doesn't fit the carryon policies.