Your most welcome, i would also recommend you Chiang Mai if there wouldnt be the smokey season. Bjt with smokey season for me uliveable with kids. Would be a good option if you would bave a second home somewhere in the south for example so you could escape for some months. But with kids, visiting a school, nearly Impossible.
Im living with my son in Khon Kaen. I love the peaceful vibe without all the Tourists. Everything here what you need. It also has an international school. (California Curriculum). Also some bilingual schools available. Huge University. All the good Hospitals. Beautiful Markets, Lakes and Parks. Beautiful people
Yes he could work in Thailand. Here in Khon Kaen there are a lot of foreign teachers. When you work for example as english teacher the school or agency will clear things like work permit and Visa for you. Maybe he could try to find a job as french teacher. Guess there are also french schools in Thailand ir also goverment or private achools that offer french lessons. Another option would be setting up your own bisiness and get him a work permit about the requirements you can find many informations online.