Good Riddles

Question: I have two rings. I move by request. If the mixture isn't right I just sit and rest.

What am I?

Question: I do good things, but one small push could be a horrid disaster! I am normally used for decoration now.

Question: When the answer I give is yes, it is no, and when the answer I give is no, it is yes. What is the question?

Question: Where do all the letters sleep?

Question: Lil Johnny's mom has 4 sons named Nickel, Dime, and Quarter: What is the forth sons name? ( And it's not Penny 'cause that's a girl name.)