Seeking “Power to subpoena” in State of Washington.

I am in the process of getting custody of my sisters children. I have already been given temporary custody with both parent's approval and both parents signing on as joiners. The temporary custody was an attempt to give them the chance to clean up and change their ways, but both parents have refused to do so and continue to use drugs and abuse the children. They have also refused to follow the current orders, with one of these instances resulting in the police having to be involved to force the return of the children.

At the time of signing the temporary orders the plan was for this to only be temporary, and because the parents were not going to fight I didn't expose their past. But now that I am following through with the permanent papers I expect the parents to fight somewhat. I have already gathered proof of general neglect, medical neglect, nutritional deprivation, and abandonment. I am now trying to prove the years of drug use, but I will likely need to subpoena their medical records from a few different doctors and their pharmacies records to do so, as well as somehow force the father to submit a blood test and the mother to submit a hair sample for testing. I do not have a lawyer, nor the money to get one.

I learned from the court clerk that I could motion for power to subpoena, but of course she wasn't allowed to advise me on how to do so. How do I go about doing this? What sort of evidence would I have to show a judge to be given this "power"?

Other topics of interest that I would like to know about:
Washington Family Code as shown here http://www.able2know.com/forums/a2k-post955294.html#955294 for Texas
Legal aid for minors in Washington State

Thanks in advance