Basically apply this method and you shouldnt go far wrong in identifying the problem:-

1) Check fluid level and condition of fluid.
2) Check master cylinder for leaks.
3) Check all brake pipes for leaks.
4) Check the calipers and rear cylinders for leaks.
5) Check the condition of the flexi pipes - if you still have rubber ones seriously think of upgrading to braided. Def worth the cash and stops the pipes flexing under pressure.
6) Check the rear load valves (if you car has them) - they may well have seized and only let a small amount of fluid through as well as possibly trapping air in the system giving the spongy feel on the pedal.
7) Check the abs modulators (in the engine bay behind the engine)

I know you have replaced/changed some of the above but always worth checking again.

If all the above is ok - bleed your system and remember

a) Leave the handbrake off
b) Make sure the car is level and under load especially if load valves fitted to the rear when bleeding.