Your parents can file a petition for nonparental custody. Those forms can be found at www.courts.wa.gov. It's going to be an uphill battle, however, if the child is living with his mother and there are no issues that have caused CPS involvement.
To my knowledge, there is no form that you can fill out that would essentially make your parents the "other parent" in your place, if that's what you're asking.
Please note that this answer is the best I can do with the limited info I have; you may want to consult an attorney further about your specific situation.