Brake Failure - Twice

When you say total brake failure, if you mean the pedal went straight to the floor with no resistance it has to be brake master clyinder as most modern day cars have a dual system and if fault any where else the pedal would meet resistance near rge bottom.
If later is the case, clamp of the wheel cly. In turn using a brake hose clamp or if used cafefully a set of mole grips (vicegrips) clamping each wheel in turn until you isolate the offending wheel cly.
If it is the first option you should check the rear of master cly. Where the push rod goes in usually behind brake pedal you will normally find a little dampness but not always as it can be sucking air. When it is the master cly. If you drain fluid and refil it is difficult to bleed system as the rubbers in cly. Colapse when pressur is released hope this helps