I'm talking generally to see if he can live in Thailand for one year or for an extended period. Some people holidaying love Thailand, but living here especially after dropping USD 20k and hating it is an expensive mistake. But we are not all rich like you.
Easiest to do it in Thailand but you may want to try a one year education Visa first to see if that works for you instead of putting all that money out there and then finding it doesn't work for you.
No consulates are giving dependent visas for kids so don't worry if they're all under 15 you won't have any problems at all.
It's a Ministry of Foreign Affairs problem and immigration don't care about kid's overstaying. It's just another stamping that passport which will disappear in a few years when they get a new passport.
Any visas can be scam visas even retirement visas old men! If you're not going to immigration yourself, in your own province then you're getting a scam visa.