How is violin playing in The Metamorphosis significant and is Gregor's eating problem related to Grete's playing?
There may be...Grete is unable to play the violin freely and beautifully until after Gregor is no longer the sole breadwinner of the family. For some reason, her playing was suppressed and forced.
After Gregor becomes an insect, he is free of the oppression of the working world. However, he now is imprisoned not only in his new body making it nearly impossible for him to eat as he once did, but also in his room since his family can't stand to look at him. He complete alienation "frees" the rest of the family from their invisible bonds...they actually get jobs, become productive, and live normal lives.
It is rather like a Phoenix...out of the ashes of Gregor's death come the new and shiny versions of his mother, father, and sister. Why they couldn't be this way before, saving Gregor the pain and suffering of being an outcast and dying a horrible death remains an unanswered question. Perhaps, like Jesus, his ultimate sacrifice was needed to save the rest of the family from themselves.