Make sure your partner has already cancelled the work permit and Non-B visa.

He needs to go in person. If he cannot attend on the appointment date, he should go to Immigration as soon as possible afterward. Someone else cannot usually go on his behalf.

When you are in Laos, just apply for non o visa(single 3 months) via the website . The important is you have to prepare the document files well such as the current location(hotel you live in Laos), the marriage certificate, the bank statement letter that shows the money more than 400,000 baht and longer than 3 months continuously(foreigner bank in English can be ok).

A 5-day overstay with fine paid usually is not a serious issue. However, recommend applying for a tourist visa in advance for smoother entry.

You can now apply for a visa via Thai e-Visa. For your case, apply for a single-entry Non-O Marriage Visa, then extend it for one year after arriving in Thailand. It seems that there is no need to use a Yellow House Book, and you can use an English bank statement from a foreign account.