I have a seven year old sister

- So keep your nude activities to your own bedroom and don't expose yourself to the other members of your family.

I don't know what "needs to my parents" means. Do you need to tell your parents you prefer to be in the nude? So tell them in exactly those words. Tell them you will keep your choice to be nude to within the confines of your house.

If your sister somehow manages to see you nude and it's other than an innocent situation I would expect some very big problems to come your way.