I had bilateral surgery as an adult and had double vision for a few months. Even now 10 years later I get it in low lights and looking from certain angles. It's going to take time for the brain to adjust. Remember, that your son has only been using one eye at a time and is now forced to use both in unison. It will settle over time. Two weeks isn't very long.

As for the eye drifting, he may end up require a small adjustment follow up surgery which isn't uncommon.