There is a separate Facebook group for Thai citizenship and residency. They are probably a better audience for this question.
I’m pretty sure you have to have worked and paid taxes in Thailand for at least 3 years. That makes me ineligible so I lost interest in the subject and exited that FB group
OK. There are multiple types of LTR. I have the pensioner LTR which is easy to get on your own. The one you want might indeed need a lawyer. Sorry, I can’t help you.