Board Thread:General Discussion/@comment-4287993-20170516070506/@comment-31292614-20170902231442

Technically, they are step siblings, but related only through marriage, not by blood. It also should be noted that Maggie is Richard's BIOLOGICAL child, and was adopted, so she really isn't Richard's child, therefore not being a usual stepsibling. Richard and Catherine also married when the Jackson and Maggie were adults, and not children, so I don't think they view themselves as "siblings" as not growing up together, etc.