Brakes on all four tires now the brake paddle is soft?

All right. One in a row! Happy to hear you can safely buzz off into the sunset. I mean "sail off", not buzz off!

A faulty booster will give you a very heavy and hard brake pedal, to test booster, with engine off, pump pedal until it becomes hard, hold foot on pedal and start engine, pedal should suck down a little, I would be thinking that you have air in the system, so start with a bleed and see how that works, if you cant see any signs of a leak, pull the master and check the rear seal, often you get a leak there.

This does not make any sense, I can't see here there would be any connection, so to isolate the two items that may be connected, disconnect booster vacuum and plug line, try starting with brake depressed, and disconnect brake light switch and try a start and see if there is any change.

Try rebleeding your system or have a pro do it. Make sure master is full when you do this.

If the pedal is dropping under light pedal pressure, you may have a bypassing brake master cylinder, if you hold firm pressure and it stays up look into this as well.

There is no visible leaks, the lines have been bled and the pedal still goes to the floor, Does the pedal go to the floor with the engine not running and can you pump them up? Has the master cylinder every gone completly dry? Lets try bleeding the master cylinder itself first. With the engine not running you should be able to get some brakes when you pump them up.

You need to look in the dust boots of the calipers to check for fluid that hasn't made it all the way out!
Try this first tho. Get 4 brake hose clamps and clamp the hoses at each wheel. Now step on the brake pedal if it still goes to the floor you either have more bleeding to do, or the master cylinder is NG, If you have a good pedal, take the clamps off one at a time and check the pedal each time, you will find the bad spot this way! When you make it to the leaky caliper removing the hose clamp will cause the pedal to sink to the floor.

When you bled the brakes was all the air removed from the lines? I agree with merlin, I could be wrong but something is telling me that there is still air in the lines. Try bleeding each wheel again.

Bleeding the lines. Do one wheel at a time. There are a couple of diferent ways people do them. Get a small piece of hose. The size that fits over the cap of the bleeder valve and put it on the end. With the other end in a bottle or can with brake fluid covering the end of the tube. Have someone pump up the brakes a few times until the pedal gets harder. When the pedal gets hard the person in the car keeps a steady pressure on the brake pedal. The one under the car bleediing the brakes opens the bleeder valve a little the person in the car will feel the pedal go down, they would keep pressure on the pedal until the one bleeding the lines lets them know the valve is closed and they can release the pedal. Meaning that you have closed the line. If one lets the pressure off the brake pedal before the valve is closed, it could suck air back in when the pedal is released before the bleeder valve is closed. With the end of the hose in a can with brake fluid it is less likely that air will go back in the line. Bleed the lines until you don't see air bubbles comming from the covered hose in the can. When the bleeder valve is closet the person in the car pumps up the brakes again. Then they hold the brake pedal like before. Continue bleeding the brake until all the air is out, after the brake is bled proceed to the next brake. Keep checking the brake fluid resevior so it does not run dry. Keep filling it each time you bleed each wheel.