One could never capture the whole beach boys story in one film
What they could do is make one documenting the Pet Sounds-Smile-Smiley Smile period. Just a feature documenting Brian's pinnacle and downfall, could be great if executed well and they get all hands onboard. Mike would either stop it or VDP would refuse his lyrics again....
I think you can properly tell the Brian story while being respectful to everyone. Hopefully the others get on board, if they're even in it.