Okon, I'm not sure I can answer your question fully, but I will try to give you some hints. First, we refer to "brake" (to stop a vehicle), not "break" ( to disconnect or to come apart). Second, the brakes should work properly with or without ABS operating. ABS will try to correct for one or more wheels sliding while braking in order to maintain steering control. You could have one of several problems: 1) air trapped in the brake lines - will make the pedal feel "spongy". Bleeding the brake lines is a tricky job best left to an expert mechanic. 2) faulty master cylinder - this is the heart of the system - when you press the brake pedal, you develop pressure that is distributed to all four wheels. If the master cylinder leaks, you could get good pressure when you first press the brake pedal, and then lose pressure as you hold the pedal down. If that were the case, your ABS would not work well either, because it relies on the master cylinder to maintain pressure. Finally - one or more wheel cylinders (that actuates the drum or disc) could leak - this might cause similar issues as faulty master cylinder. ( Look up "Hydraulic brake system" online to see a diagram of the system and to understand how the parts interact).
You do not state how many miles are on the vehicle and the brake system. If it is a high number, the brake wear may have allowed the wheel (piston) to extend to a part of the cylinder which is not worn as much, or corroded so that the hydraulic seal is not good. If you have installed new discs or drums, you might have to rebuild the wheel cylinders. This is not a fun job, but it is something you can do. Check internet for instructions.. The important thing is to keep everything VERY clean. you do not want any dirt particles in you brake system. After rebuilding wheel cylinders, you will have to fill and bleed the system with new brake fluid. I hope this helps