I'm taking my parent's gun from their safe while they are sleeping.
Do your parents have many guns?
My parents have few guns, only for self-defense.
It is good to be prepared but you shouldn't take the guns from your parents safe. They are responsible for them and could get in trouble if you got your hands on them and did something bad. You can ask them for permission to use the guns instead.
I'll make sure my parents won't find out.
You shouldn't hide things from your parents. They have a right to know what things you take of theirs, as you should ask their permission. If something happens with the gun while you have it, they could get into a lot of trouble.