Is a single piece of advice sufficient to abandon backbiting and listening to music, or should it be repeated to relatives and friends? And does sin befall one who remains silent without advising her friends when they mock someone?

We congratulate you on enjoining what is right and forbidding what is wrong, which is an obligation upon every Muslim according to their ability. Changing what is wrong is done by hand; if one is unable, then by tongue; if one is unable, then by heart. Denouncing evil may be a communal obligation (fard kifaya) or an individual obligation (fard ayn). We advise you to be patient with your family and continue to advise them gently and wisely. If you hear your friend mocking a teacher or anyone else, advise her. If she does not comply, then distance yourself from that gathering, otherwise, you would be a partner in sin. Finally, the phrase "pleasing the spirit of Allah" is incorrect. The spirit is not among the attributes of Allah Almighty, and the addition of "spirit" to Allah Almighty in some texts is an addition of possession and honor.