If its just a regular Zetec or similar spec, then it has drum brakes in the rear. The rear shoes self adjust, or should do more like. If they don't or the drums are full of brake dust then you will get a lot of travel between the shoes and the drums. This travel is taken up by the brake pedal obviously and leading to what might seem like spongy brakes.
You'll need to remove wheels and adjust shoes either through hole in the drum or by removing the drum altogether, cleaning down with brake cleaner and adjusting. Also check front discs are not lipped, another cause of brake travel. Also check pins that the front calliper slides on. If these are stuck you get issues also.