Paternity testing - alleged father - him or his brother... can anyone help?

We are testing for paternity on my son who is 9 years old.... 10 years ago I had sexual relations with 2 brothers, plus a couple of other men. Yes, it is obvious that I had no boundaries or real guidance in my life at that age. This was 10 years ago, and just for the record, I am a completely different person now. But on a hunt for my sons father, I decided to test the one I had sex with more often. We can call him Brother A. When the results came back that he is not the father, they sent me the DNA results. Out of 15 alleles, only 6 did not match. Leaving 9 that did. Does this mean that he could be a relative? We are testing Brother B as well, I'm just trying to do my research in the mean time. Does anyone know about DNA testing enough to help me out here? I jsut want my mind to be at ease....