Q: No brake fluid is getting to the rear brakes

I have been trying to figure out why my rear brakes are not getting any brake fluid. This problem just occurred this week. I had to replace the master cylinder and also the front right caliper because someone put power steering fluid instead of brake fluid in the master cylinder. My van has an ABS system. Before mounting the master cylinder, I pressurized it. To try to gravity bleed the brakes, my friend and I put the van on level ground and all four bleeder valves opened at each wheel. However, we could not get any fluid to come out at the rear brakes. So we closed the rear bleeders and worked on the front brakes, bleeding them individually and the process went well. Then, underneath the van, we disconnected the brake line that was going to the rear brakes. No brake fluid! I am wondering if the problem is the proportioner valve and if it has rubber seals that might be swollen up from the power steering fluid. Or, I am wondering if I should bleed anything on the proportioner valve. I am an amateur mechanic and have a little knowledge about car maintenance and repairs; however, I am not educated regarding the ABS system. I can change the brakes and lines and things like that. My van has front brakes and since I put on the master cylinder, the brake system light and the ABS light are no longer illuminating. But it seems illogical that those warning lights would go out when I do not have rear brakes. My van has disc brakes on the front and on the rear there are drum brakes. I would very much like to perform the repairs myself, if possible. I have to travel 2 hours a day to/from work and I really need to get this figured out. One more thing: we did not replace the front brakes because we assumed that the lines are not swollen since we were getting fluid from the bleeders. In your professional experience, what can my friend and I do to get my van in good running condition?