Doesn't seem you would be able to change your brother-in-law's mind.
If he must have on-wall speakers, I think five NHT Super-Zero speakers + dual subwoofers would very good. He could get white speakers to match the wall if he likes.
Or other small bookshelf speakers that can be wall-mounted with a bracket.
I can vouch for Denon AVR. But it doesn't seem like he will change his mind anyway.