I think you will find, from the excellent information provided by FL_engineer, that Mudafer Yassin had/has two brothers...Moyser and Moffak. The Yassin (or Yasin) family hails from Mosul. Arab society is tribal. The Yasin family, give or take a brother or two, would still be just where they always where.
What did he do for a living? Do you mean before or after he worked for Saddam? (Sorry, just couldn't resist!)
But, where is Mudafer Yassin? Did he and Michael's sister live in the U.S. or in Iraq? Obviously, Madafer is not in Mosul or Nick would have visited his uncle-in-law instead of his uncle-in-law's brother. There is no mention of Nick visiting his uncle-in-law while in Iraq, which leads me to believe that Madafer is not in Iraq. If still alive (and we haven't heard he's dead), he is likely in the U.S.
So again, where is Mudafer Yassin?
Yes, I read the "excellent information" from FL_engineer, but that just told me there are a whole lot of Yassin/Yasin family members around, many of whom are up to no good.