I would be please to here your 2 cents on this :

mother and father in law's, both Thai but not married

want to buy a house in the US (they have the means)

and retire there or at least spend several months per year overthere

anybody have experience? familie in laws who did the same ?

Belg

Do they have any immediate relatives living in the U.S. who are American citizens?

If not, then they might look into getting a U.S. TOURIST visa, for which they would have to prove that they have good ties to Thailand and really do intend to return to Thailand. If they own property here in Thailand, and have immediate family here, such as sons and daughters, and even better if they own a business, then they will probably get a U.S. tourist visa.

People visiting the U.S., even on tourist visas, are usually able to purchase property, houses, townhouses, condos, etc. Especially if they are going to be paying in cash!

Mac