I have had some strange issues when the wing fuel tanks get low. I am sure that I am not doing something right or have something set up wrong. So last night I am cruising around FL320 The wing tanks get down to about 500 lbs a piece, so I opened up the crossfeed valves so that engines 1 and 3 would feed from the center tank. Okay no problem things are going fine. Then engines 2 and 3 die. So I did a air start on them and they fire right back up. Then all three died.  Did and air start on 2, it started went full throttle. Did and air start on 1, it started and went full throttle. Did an airstart on 3 it started. So I put all three engines to standard climb power. Unfortunately within 2-3 minutes they died again. As I glided towards the ground without control, because for some reason even though the APU was providing enough electrical power to run the hydros the flight controls still wouldn't work unless an engine was running. So.... what did I do wrong?

You would have lost system A hydraulics with no engines but still had control of the primary flight control surfaces with manual reversion in the real plane. I guess CS didn't model manual reversion in their simulation. The APU isn't approved for in flight use. And the APU will only supply electrical power to system B electric hydraulic pumps which don't power any primary flight controls except the upper rudder. The only thing system B powers is the brakes, inboard flight spoilers, upper rudder and the aft airstairs.