I think they left it open-ended because of the fact that he got people dead, not cousinhood though.

Remember Russian classics - they used to marry their cousins in 19th century Russia, easily!

Yup, growing up on that and Victorian lit, it took me years before I even realized this sort of thing was odd. Btw, cousin marriage is legal in one-third of the states (which means it's valid in all) and I don't think there are any laws against stepsibling marriage, here.