Originally Posted by DigificWriter
Singer flat-out said that Alex and Scott are not brothers in the filmic universe. This is backed up, BTW, by the idea that, although not identified as such, the boy with sunglasses from the Cerebro montage was intended to be Scott, but even if you dismiss that idea, you still have to deal with Singer's statement.
With the same surname and even a similar-looking power manifestation (on screen anyway, not so much in the comics), they must surely be related. The same father, at least. Singer may well backtrack on his initial insistence that they are not brothers. It's possible for them to be brothers who, as in the comics, were unaware of each other's existence for many years.