I'm 23 years old and I can't sing in the same house as my parents.
Why dont you like to sing while in the house with your parents?
I don't want to hear my parents making fun of my singing
If your parents are making fun of you, it may be easier to ignore them until you have a private place you can sing. Otherwise, sing like no one is listening and when they laugh at you, laugh back.
They always listen, they'll even stand behind a closed door to make fun of me.
It sounds like your parents are the immature ones in this situation. It's okay to be upset by their negative behavior. Have you ever told them how much it hurts to be made fun of?