Just purchased the vehicle and currently with the rear seat cushions in, the rear seats fold down to maybe 10-15 degrees and don't really lock in place at all.

Is this even possible?

 

The rear seats are hinged on the forward edge. You swing them up from the rear end then drop the seat back.
There's a catch under the seat bottom which grabs the seat back and stops it. Voila', you're all flat and ready to load
NOTE: There's no need to let the seat back bang hard into the catch.