Is the tourist visa for my parents a 60-day or a 90-day visa and what are their options if they're overstaying?

You have to look in the passport....The make a stamp if you come in.... That shows the number of date how long you can stay in Thailand

@Seth ***********

, face it your parents aren't the first foreigners to overstay their visas. They probably got an "admitted until" stamp of the 4th of March, is that right? If so they'll be on 8 days overstay when they go to the immigration office and owe 4000baht in overstay fines.

They can apply for the 30 day extension right after they pay the fines for 1900baht BUT that extension will start from the expiration date of their original stamp.

The immigration office doesn't care if they act contrite or say they didn't know or even if they know how to do the action known as the "wai". Like I said your parents ain't the first foreigners to overstay here. They just want tme to pay their fines, get their extensions and be on their way.

60 day visa available to extend 30 days. what is the exit stamp saying for a date?

a Single Entry Tourist Visa is valid for 90 days as you can see on the Visa, you have to enter Thailand before the "Valid until" date to use the visa. On entrance the visa got stamped with "Used 03 Jan 2018" and they got a new stamp with the text Admitted to Stay ../../.. (date 60 days later). Now in overstay, report Monday morning at local Immigration Office, make sure they have each 500 Thb a day (counted from daystamp in passport as Admitted to Stay) to Monday 12 March and 1.900 Thb for the Extension of Stay. They will get the Extension of 30 days starting from the Admitted to Stay date.

what date is on the Until stamp when you entered Thailand?

Used 3rd January so valid until 60 days from then.

60 day, the valid until date is how late you can start using it from!