brake pedal goes to floor

you probably have a broken line and is causing the leak have a mechanic fix this and tow the car to mechanic. More than likely it has rusted through.

would one broken line cause the car to not have any braking capacity? is there any safety feature where if one line fails the other line stops the vehicle?

yes that is supposed to happen, but if brakes in back are worn or you broke a line going to back they still will not work especially since you said your master empties almost immediately. so it may be broken between ABS and master cylinder. if you have ABS the fluid may be leaking faster than it can apply the brakes.

Thank you.