As per Thai Embassy in Vientiane website, should be open, since their Calendar Updated on 2 October 2023, states that they will be closed on 8 December 2023 instead.
However, for this year's Lao National Day (2 December), the Lao government will be having a Substitution Day on Monday, 4 December 2023. As to whether Lao National Day 2023 affects the holiday closure of the Thai Embassy remains to be seen....
If you arrive into Thailand via Air, then no need for a Thailand Arrival-Departure Card (Form ตม. 6). However, if you arrive into Thailand via Land, then you still need a Form ตม. 6
True! However, the foreign passport would still have a 'stay permitted up to' end date stamped according to how these unique, special case dual nationality/citizenship/passports entered into Thailand (usually visa exempt, but there are cases where they may have a Thai visa)....
Nevertheless, hopefully, it will be a straightforward process for them to enter Thailand with an Aussie passport and carry both their expired Thai passport and current Thai ID card
No, a recent Memorandum issued by Thai Immigration Bureau would be that Thai citizens using foreign passports to enter Thailand would be treated as Thai nationals (and not considered overstay when exiting): also negates the need to get a 1-year extension as a Thai national....
Referencing Memorandum # 0029.161/ว 3263, dated 22 August 2023 (2566) of the Thai Immigration Bureau (สตม), highly suggest to carry your current Thai ID Card, along with your expired Thai passport for entry into Thailand using your Australian passport....
No problems about visas since a Thai visa is not necessary for transit within Suvarnabhumi Airport....
But, 80 minutes for transit and luggage transfer between 2 international flights at Suvarnabhumi Airport = you (transit passenger) may board the connecting flight in time, but there is a risk that your transfer luggage may not get transferred on the airplane in time....considering early evening (5pm-6pm) arrival and departure is a busy time....
