AWD question

[jeffs92svx]

I dont know anything about our awd system. This morning me and the wife were out in the snow. I have pretty much bald all season tires on the svx. Amazingly it comes out of my drive way and up my huge hill and it is slick. My question is, I had my wife to stomp it while I watched in the walmart parking lot and the two drivers side wheels spin but only the front passengers side spins. Does anyone know if all 4 are supposed to spin. We dont it a couple of times and the same results, the back passenger side wouldnt spin. Thanks.