Another thing is, do you want your daughter to have a chance to live in Thailand long-term in the future?

If yes, you have to cancel her extension officially before she leaves Thailand. To do it, the stamps have to be transferred to a new passport.

(I cannot come up with a reason for her extension that is not required to be cancelled, such as "being over 50" <- no reason to cancel)

If an old and "supposed-to-be-expired" extension is remaining, it will cause an issue when the holder wants to apply for a different extension in the future, even after years have passed.

Same for you, if you are on an extension currently, and there is even a slim chance you will be back to Thailand as not-a-tourist, you should cancel your extension officially before you leave.

If none of you will ever be back to Thailand other than a tourist for short holidays, you can just leave.

@Michael **********

, yes, your landlord is supposed to provide one.

You also need a TM.30 receipt with your current address in Bangkok.

Don't worry about TM.6 if you don't have. It's been suspended for years for travellers coming by air.

You have to go to the Chaengwattana office, Government complex building B.

The One Bangkok office wouldn't deal with 90-day reports unless your extension has been issued by BOI/IEAT.

If your son didn't get an overstay stamp before when he was overstaying, he got just lucky.

@Peter ***************

, to have to do if you are on Non-OA visa.

@Peter ******

, there is no "first month" limit.

@Gui***

, if you will do volunteering for an organization, it will be a Non-O for that like kind of employment as volunteer, with work-permit.

If you will work for a standard company, no Non-O for employment.

@Andy *****

, departure information fields are not mandatory (they are without red stars). You can leave them blank

@Brian *******

, Check your passport to see what you are on now.

If you are still on the entry stamp from the visa (90-days for Non-O for over 50, or up-to-365-days for Non-OA) with an actual visa sticker or eVisa PDF

-> The same as OP, you cannot transfer your visa. Carry both passports until the visa itself expires.

If you have already applied for a 1-year extension at the local immigration office (read the stamp)

-> Different from OP's case, you have to transfer the stamps to your new passport.

A visa issued by a Thai embassy or consulate cannot be transferred to a new passport. You have to bring both passports until your visa expires to enter Thailand on your visa.