Lisa Engle (formerly Lisa Brewer) is the ex-wife of Kristy Thomas's stepfather Watson Brewer and the mother of Kristy's stepsister Karen Brewer and stepbrother Andrew Brewer. She marries Seth Engle between books #1 and #6. (In the first printings of #6, they're referred to as Sheila and Kendall; their names were corrected in later printings. The names Lisa and Seth were probably introduced in the Baby-sitters Little Sister series.)
Lisa Engle is a stay-at-home mom, although she sometimes substitutes for Seth's assistant at his carpentry workshop. In the beginning of the series, Karen and Andrew live with her (and Seth) except for the two weekends a month they spend with Watson; in BSLS#48, Karen's Two Families, they begin spending alternate months at each house. Lisa calls Andrew "Andy-Pandy" sometimes.
Karen calls Lisa and Seth's house "the little house" (as opposed to Watson's mansion, "the big house"); they live on 12 Forest Drive in Stoneybrook.