When the whole trip out and back in to Thailand to a family of four costs a small fortune, better bother with a few possibly unnecessary documents or additional minor expenses than risk being refused boarding / entry.
Everything in this scheme - flights, hotels, covid tests - must be prepaid and is non-refundable (a main reason by the way why this kind of sandbox or AQ schemes will never bring any significant amount of tourists to the country. The second major reason being the complication of it all).