In the text shown in the question above, we can see a conflict between two characters, where the main character refuses to do what his mother asks, but the mother doesn't give up and insists on ordering the main character to do what she is asking. being requested. The cause of all this conflict is a piano. The main character refuses to play the piano again, but her mother refuses to allow her child to stop playing the piano.
"Today nobody brought his or her instrument" is correct. It is common for people to use "their" in a sentence like this, but "his or her" is the more proper term.
"Politeness is half good manners and half good lying" because when someone asks you how you are, you politely reply 'I'm doing good/well' even if your not - a lie. :)
