The 1947 novelty tune “I’m My Own Grandpa” has become shorthand for Jerry Springer-style family intrigue, but I mean to evoke the exact opposite when I say that Ruth Wilson is her own grandmother in the fascinating Mrs. Wilson. The 3-part series, airing in the U.S. on PBS, is a lightly fictionalized account of a scandal within Wilson’s own family that only became known after her grandfather’s death in the mid-1960s. It was then that his wife, Alison (portrayed by Ruth Wilson) began to unexpectedly unravel her husband’s mysteries when another woman …