“The South Rim is more commercialized than the North Rim, but does that mean that it's any less spectacular?”
The South Rim isn’t “commercialized” and it’s just as scenic as the the North Rim. Personally I’d skip the summer and only go in the other three seasons. If you or your family get bored easily in this beautiful, historic, fantastic area, stay three or four days. “Been there, done that.”
“I'm into photography so I could easily spend all day wanting to do my thing,..” It’s your vacation, Dad. Your family should let you take your photographs. IMO you don’t need to entertain them.