Yeah the 6 month multi entry visa is only necessary if you want to border bounce and just stay in Thailand. A good option would be get a single entry for 60 days. Can see alot of Thailand before you move into other countries and not have to bounce in and out all the time. Also gotta keep in mind if you run up 90 days on exempt entries, you'll almost certainly be denied trying to get back in again without a visa
that's sadly how the bureaucracy of different nations can mess you around. Sadly it will likely cost him all the fuss of going back and starting all over again. I wish you both luck.