All doors unlock, including fuel inlet and trunk, when you unlock the driver's door.
All doors lock likewise when you lock the driver's door.

I doubt the rear door opening has something to do with the vacuum locks, but you can always locate the vacuum tube going to the door and try blowing/sucking into it to see if that has any effect. More than likely, there's a linkage disconnected in there.

You'll really need a vacuum tester- everyone here loves MityVacs- to troubleshoot the vacuum locks. Good luck!

__________________