This is kinda common and isn't really an ABS issue. Part of it has to do with the pad compound and the other is nature. Basically your dad has been putting the car away "wet" without really drying the brakes. So what happens is that a thin layer of surface rust will form on the rotor and depending on the metallic levels of your brake pad compound, on the surface of the pad where it meets the rotor. So, in essence, your pads have stuck to the rotor or seized itself to the rotor. I would suggest taking the car for a spin around the block after washing before putting the car away. That should cure it of any pad sticking issue.
Oh, and it's more prevalent if it was put away wet and parked with the hand brake up