Nikolle,
Infertility is certainly quite prominent amongst males with CF, affecting ~98% or so (guestimate). They generally have something called CBAVD (congenital bilateral absence of the vas deferans). However, it certainly does not affect every male with CF. If the number is 98%, that doesn't mean that there's a 2% chance that each male with CF can impregnate a woman. It means that 2% of them are able to, and 98% are not. If your brother has 2 known CF mutations, any child he produces will get 1 of those mutations. So if a baby is born, and is not a carrier, that would certainly raise suspicion. You certainly have access to a genetics counselor (Ambry genetics) on this website. Your brother should probably consult with one as well as a urologist.