Welcome Scott,
That's pretty caring of you to think of his needs.

...unless yer doing it to be the "right" brother.
Sorry, but there aren't specific codes or even the tile police that can force him to change his ways. Though a failure that costs a pile of money may make him look real hard at what went wrong if a floor were to "tent" on him. What the industry does have is the TCA Handbook that publishes methods of installation. It's referred to in the industry as its bible.
Drag 'em over to the site. If he wants to never be wrong, he owes it to himself to benefit from the knowledge that's freely shared here.