What visa do I need to study Thai language in Thailand, and what about my family members' visas?

You're very welcome :) I hope it all works out for you.

No, sorry. Never heard of any family tree thing. I reckon you should still talk to a Thai lawyer. Tell them the whole story (maybe substitute the phrase 'false name' with 'different name'?)

I'll bet it's not the first time they will have heard of such things and the main thing is to establish your mother's Thai citizenship, not whether or not she used the right name or not.

It might be worth sending these guys an email

By the way, it won't save you hassle, it WILL BE HASSLE lol

But once it's done, you're all set for the future. Anyone who's mother is Thai is also Thai. That's the basic premise. Proving it, in cases like yours, is where the hassle is.

Ok, so the search would begin in the Amphur (district office) in Khon Kean. Thai bureaucracy is sometimes annoyingly difficult to deal with, although it's quite thorough, and they are inclined to require people to physically attend in order to get things like this done. You might need the services of a Thai lawyer if you wanted to get this done from the UK. You will need as much information as possible. Her full name, date of birth, the area of Khon Kaen where she was born, and then take it from there. How's your Thai language skills?

There's going to be a bit of detective work required, but in the long run it will be worth it.

The fact that she had an ID card means that there are records of her birth, and the fact that she is a Thai citizen. Tracking that all down is another story. Where was she born?