I want to have 3 to 4 mic with Google Hangout on air

We want to have 3 or 4 lavalier Shure SM93 mics into the Steinberg UR44 with Google Hangout on-air. We made a test and it looks like Mic 1 and Mic 2 works but nothing can be heard on Mic 3 and 4. We are using the driver from Steinberg on a Mac. Of course the UR44 is connected to the Mac through the USB. We need at least 3 or 4 mic working on Hangout to keep this product.

Martin Brossman