We have good brakes when were goin straight but.

That sounds like a loose wheel bearing may be pushing the piston in when leaning on it through a turn. There really isn't anything else that could change when the wheels are turned. Unless something is leaking fluid.

Unless the ABS is kicking in, it's a closed system and the fluid has to go somewhere.

Probably start out by pinching off individual wheels to isolate where it is occurring. You could have an internally ruptured flex line that is swelling under pressure.