Tex Johnston is a really bad example of how to do things right if that's what you're trying to do.
I have about a hundred hours in a Focke Wulf 149D. It's unique in that it allows up to 4 occupants to wear either backpack or seat cushion type parachutes while being aerobatic with each and every seat occupied and could be loaded perfectly happily to do so. I sure wasn't giving instruction to the passengers in the back seats. At the time I didn't have a CFI so I wasn't giving instruction to the passenger sitting in front. Very much legal, thanks.
You'll find that most purpose built aerobatic airplanes have 1 or 2 seats. The Marchetti SF260 has an option for a third. There are aerobatic models of Bonanzas though I've never flown them and don't know their limitations for being loaded for aerobatics so whether or not they can practically carry passengers (for CG or whatever other reasons) I can't say but they have up to 6 seats.
A passenger in the front seat of a Pitts doesn't need to be receiving instruction to sit there. Nor an Extra, nor an Eagle, nor an RV, nor an Acro Sport, etc. etc. etc. I didn't need to be giving instruction to other pilot in a Yak 52/52TW to go upside down. I didn't need to be receiving it either. I didn't need to be a certificated pilot for that matter.
Shrug.