You probably already have the answer by now. John W. LASH and his sister, Sarah, lived with William and Martha (LASH) UTTERBACK.They were William and Martha's nephew and niece. John and Sarah's parents were Lewis and Elizabeth (UTTERBACK)LASH. William & Elizabeth UTTERBACK married Lewis & Martha LASH. The parents of Martha and Lewis were John & Harriet (DECORE) LASH. You will see Harriet living next door to the UTTERBACKs in the 1860 or 1870 census, I believe.
If you haven't gotten it already, I hope this helps. Evan