You are electrically out of phase, not magnetically, but you can reverse the magnets in the neck and bridge pickups to correct this. The Stratocaster pickup is wound (top left/top going) and the humbucker and P-90 coils are wound (top left/top coming).

The P-90 and Humbucker are out of phase with the Stratocaster. You could reverse the lead wires in the Stratocaster but this would make the magnets hot and would buzz if you touch them.

Starting with the P-90 you have to loosen the bottom plate and carefully slide the (two) bar magnets out one at a time and flip them each over (180 degrees). Slide them back in and tighten the bottom plate. This will now make the pole piece polarity (North). This will be opposite of the (South) polarity of the Stratocaster. Loosen the four (4) small screws on the bottom of the Humbucker and carefully loosen the bottom plate. The six (6) adjustable pole pieces might have to be unscrewed to help release the pressure on the bar magnet inside the pickup assembly. Slide the magnet out (away from the hookup wires) and flip over (180 degrees). Replace the magnet to it’s previous position and tighten in place. Now everything will be in phase.

Note: Do one pickup and magnet at a time. Keep notes and good luck.