Going to look at a few CVPI's tomorrow. If you all had your choice in years would you prefer 2008, 2010 or 2011? I do like cruise control but 2008 sounds like it might be in the best shape. And is it illegal to put kids in the back seat if they can't open the doors? I don't mind but maybe not a great idea.
Here's some stats on the years - but the condition of the vehicle is probably more important than the year,
https://www.carcomplaints.com/Ford/Crown_Victoria/
As far as the rear door locks, I would imagine a trip to a salvage center could yield regular rear door mechanisms - plus, most cars have a switch that you can flip so that the rear doors won't open except from outside, to prevent a kid from opening the door while the vehicle is moving, so I doubt that opening from inside is a requirement.
I've seen the carcomplaints. Wasn't sure if that applied to the CVPI models. I know most of the common problems. Mostly I'm worried about the thing exploding if I ever get rear ended. Thinking of putting a rhino bar on the back..LOL. I think Ford has a $100 part to protect the gas tank a bit more but I don't think they are very effective. If I put a rhino bar on the front and the back I could drive forward or in reverse and no one would know the difference!