Well I'm gonna try something unusual here...
I'm gonna constructively critique what was posted here!
1. Kudos for having the balls to post here in the first place.
2. Anyone who even ATTEMPTS a faithfully harmonised version of any Beach Boys song automatically has my hat taken off by me - to them.
3. I think it's a fine concept, I would only look at 3 things.
Firstly, the kick must (MUST) be the loudest thing in the mix AND consistent - turn the snare down and the kick (if possible) up! If you're able, find a sampled kick that is punchier than the one you have and replace the current kick if that is an option.
Secondly, kudos on the vocals they seem quite authentic, you've captured their basic sound, I would put a touch more reverb on the backing vocals - maybe a *little* more on the lead too.
Thirdly, if that was you playing the lead guitar breaks, you're a better keyboard player than me, so I would make it your own more by playing a rocking Bar room Piano instead of the guitar sound, it's not the best guitar sound I've heard, honestly people would be more impressed with hearing a great Piano "lead break" then the synthy sound you have here, and it would be more obvious to an audience (believe it or not) that you were playing it.
Oh, and I'd end the medley with a Big Hit of theirs (maybe "Help me Rhonda" ?)
With any medley, I start and end with a big hit - start strong and end strong.
One more thing, I think you're wife has some great ideas, and IMO this was one of them!
Generally well done - keep 'em coming!