Two characters in the metamorphosis undergo a transformation: gregor, who and his sister, who select all that apply.

In Kafka's The Metamorphosis, Gregor Samsa (protagonist) wakes up to realize that he has, somehow, turned into a roach-like insect overnight. Grete (Gregor's sister) is the only one from his family who grows the strength to take care of him. While Gregor's transformation was more visible on the physical plane, Grete grew from being a whining little kid to a responsible and hard-working young woman at the end of the story. 

While the other options did occur in the story, Gregor's transformation was not a reflection of inner ugliness as he was, although self-deprecating, not a bad person. Similarly, while Grete does want to become a violinist, this is not at the center of her transformation.

Therefore, your best answer is "Two characters in The Metamorphosis undergo a transformation: Gregor, who becomes a giant insect, and his sister, who develops from a child into a young adult.