When the PCV valve is open ( vacuum in the intake manifold, no turbo boost), crankcase gases are draw into the intake manifold and burnt during combustion. This causes a vacuum in the crankcase because it is a closed loop system. You don't want negative pressure in the crankcase so a second hose is used, hose two. Fresh filtered air is drawn into the valve cover through hose two so there is no negative pressure in the crankcase.
Now when the PCV valve closes due to positive manifold pressure (turbo boost), the flow reverses. Crankcase gases flow out through hose two into the inlet pipe,through the turbo and intercooler and into the intake manifold to be burnt during combustion. So in theory you could use two catch cans, one in hose one and the other in hose two.
The majority of oil mist is drawn into the inlet manifold from the PCV valve. If you use your car at a track day where you spend a lot more time on boost then more oil mist will be going through hose two.