Popping open my instructor manual, I find nothing about doubles. I believe they are fine for AOW, student or instructor. Would I teach AOW to a student who showed up in doubles and had few dives on them? Not sure, it would depend a bit on the student. I might insist on a private class, me in doubles also, so I could model my own modest version of technique, trim, buoyancy control et et. I would definitely insist on some pool time.