Do my elderly parents need to show a return ticket at immigration when entering Thailand on standby tickets?

The main concern is whether your parents will need to show a return ticket upon entering Thailand with their Irish EU passports under the visa waiver program. Generally, while the requirement to show a return ticket falls on airlines during check-in, immigration officers in Thailand are less likely to ask for proof of onward travel for elderly travelers, especially if they have not raised issues during previous visits. It is advised to be prepared with a backup onward ticket for peace of mind, particularly since the tickets are standby and may not be secured in advance.