A new passport does not work for hiding the old anymore. Biometrics has been in use for 3 years here. A friend tried that route and got refused on arrival in Thailand.
3 weeks ago I did my yearly extension of stay for purpose of retirement, 3 days before my 1 year would expire. I live in Phuket and was at immigration less than 30 minutes.
If they flew in with no visa, they should have 30 days. Another 30 days can be got for 1900 baht at immagration office nearest them, anytime before the 1st 30 expires.
Simply put, enter Thailand on tourist visa, go to immigration here, apply for non-o, open bank account, deposit the funds, $800,000, then at end of 3 month non-o, apply for extension of stay, 365 days, for purpose of retirement. After 1 year, you can bypass 800,000 deposit if you have consistant 65,000 per month each from home country to Thai bank account. It is not too conplicated once you get the 1st 365 day extension of stay.