His first wife was Esther Tindale, married in 1839.
<ref>[
https://familyhistory.bdm.nsw.gov.au/ New South Wales Births, Deaths and Marriages] marriage registration number 292/1839. Esther Tindale; John Blackstone; district CD (Church of England: Castlereagh). Accessed 20 February 2023.</ref>
Esther died in 1848.
<ref>[
https://familyhistory.bdm.nsw.gov.au/ New South Wales Births, Deaths and Marriages] death registration number 575/1848. Name: Esther Blackstone; age: 27; district: MW (Church of England: Penrith). Accessed 20 February 2023.</ref>
<ref>Family Notices (1848, July 3). ''The Sydney Morning Herald (NSW : 1842 - 1954)'', p. 3. Retrieved February 20, 2023, from National Library of Australia Trove [
https://trove.nla.gov.au/newspaper/article/12912992?searchTerm=Blackstone 12912992]. "On Sunday, the 25th June, at her residence, Dabee, Esther, the beloved wife of John Blackstone, Esq., in the 27th year of her age."</ref>
His second wife was Fanny Margaret Samuell, married in 1853.
<ref>[
https://familyhistory.bdm.nsw.gov.au/ New South Wales Births, Deaths and Marriages] marriage registration number 971/1853. Fanny M Samuell; John Blackstone; district CJ (Church of England: Sydney). Accessed 20 February 2023.</ref>
<ref>Family Notices (1853, April 23). ''The Sydney Morning Herald (NSW : 1842 - 1954)'', p. 5. Retrieved February 20, 2023, from National Library of Australia Trove [
https://trove.nla.gov.au/newspaper/article/12945306?searchTerm=Blackstone 12945306]. "On the 21st instant, by special license, at St. James', by the Rev. C. F. D. Priddle, M.A., John Blackstone, Esq., J.P., of Dabee, to Fanny Margaret, eldest daughter of Mr. William Samuell, of Pitt-street, Sydney."</ref>
A daughter Fanny Mary Ann died as an infant in 1855.
<ref>[
https://familyhistory.bdm.nsw.gov.au/ New South Wales Births, Deaths and Marriages] death registration number 153/1855. Name: Fanny M A Blackstone; infant; district: NV (Church of England: Camperdown; Newtown). Accessed 20 February 2023.</ref>
<ref>Family Notices (1855, February 21). ''The Sydney Morning Herald (NSW : 1842 - 1954)'', p. 8. Retrieved February 20, 2023, from National Library of Australia Trove [
https://trove.nla.gov.au/newspaper/article/12965926?searchTerm=Blackstone 12965926]. "At Woolloomoolo, on the 20th instant, Fanny Mary Ann, the infant daughter of Mr. John Blackstone, of Dabee, aged six months and one week."</ref>
Fanny Margaret died in 1898.
<ref>[
https://familyhistory.bdm.nsw.gov.au/ New South Wales Births, Deaths and Marriages] death registration number 16028/1898. Name: Fanny M Blackstone; father: Frederick A; mother: Helen K; district: Smithfield. Accessed 20 February 2023.</ref>