In the legends (I know that's not all too reliable) but weren't Arthur and Morgause half-siblings?
Uther certainly has got a lot of skeletons! The thing that's bugging me is, why adopt Morgana as his Ward and yet put Morgause in such a dangerous situation that Gaius sent her off to the Priestesses of the Old Religion? They definately, definately need to come up with a feasible explanation for that. If they leave that rock unturned, I will be out for blood.