Even after replacing front and rear brakes, the pedal goes nearly to the floor (but does stop the vehicle). What do I need to do

bleed the brakes again starting at the longest line at the rear and work forward . The indication is still air in the lines.

The front portion of the reservoir has fluid used for the front brakes which provide the majority of the vehicles stopping power. There is a valve that is supposed to shift to isolate the front and rear brakes when this occurs but it doesn't always work as designed. You have lost all the fluid in the front brake system. This is due one of these possible issues:

Broken brake line
Broken brake hose from line to caliper
Leaking caliper seal

You need to find and repair the leak, refill and bleed the front brake system to get the vehicle back in service. IT IS NOT SAFE TO DRIVE IN ITS CURRENT STATE!!!

I would inspect the brake booster for vacuum leak. When the booster is not working you get a hard pedal, yet when you start the vehicle the pedal will hit the floor because of the damaged diaphram inside the brake booster.

If the car has drum brakes in the rear, Jack the rear up and have someone push the brake pedal hard and you try to turn the wheel. If you can turn it you need to adjust the rear shoes. They may be traveling out so far that the fluid level drops causing the pedal to go to the floor. You must adjust them with the drum on till you hear and feel the shoes rubbing against the drum. Hope this helps.

Tricky and risky ,and if garage is not to far away, use the parking brake and brake pedal at low speeds to stop. Taking out of gear at stops at a light or crossing/stop sign. Otherwise, cap and plug the main line at rear axle brake tee spliter from front.

check vacumn and\or connections to the vacumn boost cannister.

You have to bleed it on all 4 wheel

If you haven't already, check your rubber lines for weakness; they could be ballooning under pressure.

Thank you for allowing me to assist you, Before we do anyhing, I need some additional information.
Please respond to the following 5 questions so that I may be able to help you better.
Is you vehicle front disc/rear drum or front disc/rear disc?
When were the brakes changed last?
If so, front or rear?
If you apply the park brake, does the vehicle move at all when you put it in gear?
Finally, I am understanding that the brake pedal goes to the floor, you have no resistance on the pedal, and the vehicle does not stop when applying the brakes. Da?

are your rear drums set up? why did you bleed the brakes. when only when you installed new pads?