Audi A6 2006 3.2 Quattro 2/4 brakes work

[Isacc K]

I drive an Audi A6 2006 3.2 Quattro and I can’t figure out what’s the problem with my car. Recently I’ve been driving it and it’s been fine but the brake feels like I’m stepping on a lot of air, and the brakes are not activating. I took it to a shop and they said Only 2/4 brakes work and they have no idea what is wrong with it. Anyone know what’s going on? One brake in the front works and one brake in the back works. Please help a brother out with any possible problems with the car and even solutions.  

[Magnet]

Welcome Isaac, and thanks for joining. 
Are the working and non working front and rear brakes diagonally opposite? 
If so, could be associated with ABS-? 
‘…help a brother out….’ Masonic? 
Kind regards,

Gareth.