I think that DNA testing is in order. If Don and "Shane" do have a sister they might never have known -- family pride and all that: a good student, a sister with a doctorate, in THEIR family? Besides, they may have been told and have simply forgotten or had the knowledge washed away in the beer.

As for the other "Shane" I supppose that it could be Don's brother. Off on a bender with a friend, a fit of alcoholic remorse, joining the Trappists, the friend (and who can tell what he looks like, since greasey hair, yellow teeth, bloodshot eyes, and random beard stubble all look alike?) moves in to sponge off Don. Even the odors of stale tobacco smoke, stale beer and ancient biological mishaps would smell the same.

No, I think DNA testing is in order. Where can we get a sample of the McBride parents' DNA? All of the other four will provide it, drunk or sober. But...

What happens if we find that none of them are related? Or that Certain Familial Skeletons emerge from the closet?

Oh my, but this could be as exciting as the time Lady Pru's biscuit broke off in her tea whle she was entertaining the Governour-General!