TL, IIRC there is legal pressident(sp?) for declaring war on non country entities, Barbary Pirates 1804 or so. President Jefferson asked Congress to declare war on them, and did so.
Now If I were President I'd tell the 9th ciruit and the supremes to "Bite Me" and show me where the US Constitution gives them the authority to decide what and how the military can handle prisoners of war. And I'll show them the article that clearly states the president is the Commander in Chief ie: Head idiot what are in charge of the US Military. Until such time I'd refuse to recognize their authortiy in this matter. The supremes can't do squat, Congress can Impeach , the military can cuop, or the citizens can have an armed uprising in order to remove a sitting President.
Now the supremes may be able to show me a treaty that states the Red Cross, it's equivalent, or representative of the country that the POW's fought for can have access to them. BUT there is the "fly in the onitment" what country are they fighting for? Does that country even want to send representatives to see them?