the E-brake is a separate system from the actual hydro braking portion of the caliper. the E-brake itself is adjusted by an allen key on the back side of the caliper(be sure to let whomever know they should never attempt to push the piston back in)
from my personal experience, the only real way to get fluid to the rear lines is to use a good vacuum bleeder (not the hand pump style) you can buy various types just be weary of the pistol grip/hand style.
its 95% unlikely your proportioning valve failed. In the future I suggest using line locks on the brake lines to prevent air feedback/draining of the lines when you change the calipers.
hope this helps