- Thomas Ong 17??-?
- Martha Feast 17??-?
Mary Ong was at least the seventh child of Thomas Ong of Ely - the fourth child with his second wife Martha Feast. Despite all these siblings, it appears that Mary and her younger sister Martha, were the only two children to survive. She was also the second of these children to be named Mary.
Mary married a labourer of Ely named Philip Cross and the couple remained in Ely where they had at least fifteen children.
- Philip Cross (1770-1846) on 24th May 1790 at Holy Trinity church, Ely, Cambridgeshire.
- James Cross (1791-?) married Elizabeth Lee (1791-?)
- Robert Cross (1793-?)
- John Cross (1795-?)
- Margaret Cross (1797-1802)
- Philip Cross (1798-?) married Sarah Freeman
- Robert Cross (1800-?) married Arabella Scott
- Richard Cross (1803-?) married Ann Hunt
- Mary Cross (1804-?) married John Cross
- Margaret Cross (1807-?) married William Feast
- Kezia Cross twin(1809)
- Sarah Cross twin (1809)
- Samuel Cross (18??-1809)
- Charles Cross (1810-1871) married Jane Thompson (-1834) and later to Elizabeth Garner (-1859)
- George Cross (1812-1887) married Frances Thompson (-1841) and later to Julia Thurlow (1820-1892)
- Peter Cross (1814-?) married Charlotte Hills