1998 Ford Taurus Brake Problem Very Soft and Squeals

I am having an issue with my brakes. They were very very soft and squeal sound appears to come from the direction of the steering wheel area or under it. We were told the rear shoes and wheel cylinders had to be replaced and new hardware installed. We repaired the rear brakes by replacing the shoes, cylinder and new hardware. Problem still appeared and had the fluid exchanged because it was dirty. Then was told the master cylinder was leaking. Replaced the master cylinder. It doesn’t seem like it has fixed anything still very very soft brakes and still squeals. Any Ideas!!! The squealing occurs when pressing the brakes whether parked or moving.

You have a pressure loss in the brake system.

If you pump the brake pedal to the floor several times, does it stay soft or firm up after a few pushes? Is there fluid loss? Did you bleed the air out of the system?