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.