Some additional information if it's of interest to anyone:
Mary Jones, born 1843, may have been, according to family legend, Mary Ellen Lewis prior to marriage to John O. Jones. According to this legend, she was born in Anglesey, but that contradicts her stated birth place (Llanllechid, Carnarvonshire) on the 1881, 1891 & 1901 census returns.
Eldest son Edward Lewis Jones (b. 1870 - Bethesda) married Elizabeth (family name unknown) in 1900 and they had three children, Mary Elizabeth Jones (b. 1901), Emlyn Jones (b. 1905), and Florence Jones (b. 1908). They lived at 21 Carneddi Road Bethesda according to the 1911 Census.
John Owen Jones (my grandfather, b. 1880) migrated to Australia around 1913. He was working in Cymmer, Porth before migrating, from Old South Wales to New South Wales.
Mary Ellen Jones (daughter, b. about 1885) is mentioned in the 1901 Census as a 16 year old Domestic Servant employed by the Lloyd family at 22 Ogwen Terrace (also known as High Street), Bethesda. Dr. Jenkin Lloyd was a 48 year old Surgeon from Llanddeiniol. Mary isn't mentioned in the 1911 Census, but she did marry a chap named Pritchard in the Oct-Dec quarter 1912. I understand that they had two children, Jane & Mair Pritchard.