Did everything I can think of but brakes still soft (Honda Element 2007)

We had some extreme cold weather and my brakes started getting soft. By
the time I got home I was having to pump them to stop. I got to my home and
my fluid level was low. I figured I had a leak and searched everywhere but no
leak. I changed out my front calipers as the old ones looked like maybe they
had a bulge in the rubber near the piston and I thought maybe they leaked in
the cold weather - bled my brakes again, still no brakes. Replaced the
master cylinder, bench bled, then bled my brakes again. I get some pressure
with car off, no air bubbles after bleed, but it's still soft and not stiffening
during bleed process. When I turn on the car the pedal just goes to the floor,
if I pump it quickly I can build up a tiny amount of pressure but can't even get
enough pressure to stop car. What the heck is going on. No leaks with
bleeding or tests now - why can't I get brake pressure? I was told that with
Honda Element the sequence is RF, LF, LR, RR.