How long was the transmission fluid in the system? If for any more than a few hrs (even that may be too long) the rubber seals in the master cyl may have gone soft and deformed. When you try to bled the brakes can you get any pressure at all? If there is no pressure after a few pumps, there will be a leak some where, or the master cyl is by passing internally, if master is damaged due to oil contamination then all calipers and or wheel cylinders will have to be O/hauled. If there is a proportion valve that could be an issue as well.