Do you have the names of Richard and Janet's children in birth order?
Richard and Janet MuirThere is only 1 record of a headstone in Carstairs churchyard containing the name WallaceGavin Wallace but no date given
Robert WalaceScotland, Births and Baptisms, 1564-1950 birth: 22 January 1767 christening: 30 January 1767 , CARNWATH, LANARK, SCOTLAND residence: 1767 Carnwath, Lanarkshire, Scotland father:Richard Walacemother:Janet Mure https://familysearch.org/pal:/MM9.1.1/XTLD-KHF
https://familysearch.org/pal:/MM9.1.1/XTL6-33Thttps://familysearch.org/pal:/MM9.1.1/XTLX-H48https://familysearch.org/pal:/MM9.1.1/XTLT-YLGhttps://familysearch.org/pal:/MM9.1.1/XTLY-MZQADDEDRobert is recorded as WALACE