How much metro did you dose every day. The dosage on the label is no longer enough for Discus. We recommend doubling it and going a few days longer. We suggest 500 mg metro daily for 10 to 12 days with large WC every day. It's a case of out with the bad and in with the good.
Since the PB is the only fish showing symptoms and you've already thrown a bunch of meds at all the fish, I'd suggest moving the sick fish to a BB tank, turning the heat up to over 90 and treating with metro again.