Benjamin Fletcher Smith. Stated on death index of Thomas Smith. 
on death certificate of Thomas Smith his mothers maiden name is Knight. Mary Ann McSweeney may have had a previous marriage before marrying Benjamin.
There's a bit of doubt about this generation of great great grandparents. It is possible that Benjamin Smith was married to X Fletcher (probably a non-catholic) and X Nash was married to X McSweeney because Jane Nash was said to be Irish Catholic.
Benjamin had two children with Mary Ann Knight in Launceston, Tasmania: a son 2 Jun 1857 and a daughter 2 Aug 1858. Neither child was named at birth.
↑ "Australia, Tasmania, Civil Registration, 1803-1933," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:Q27M-X215 : 13 March 2020), Benjamin Fletch Smith in entry for Smith, 2 Jun 1857; citing Birth 2 Jun 1857, Launceston, Tasmania, Australia, line #87712, Archives Office of Tasmania, Hobart; FHL microfilm 7,368,115.
↑ "Australia, Tasmania, Civil Registration, 1803-1933," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:Q27M-F91S : 13 March 2020), Benjamin Fletch Smith in entry for Smith, 2 Aug 1858; citing Birth 2 Aug 1858, Launceston, Tasmania, Australia, line #89942, Archives Office of Tasmania, Hobart; FHL microfilm 7,368,115.
"England and Wales Marriage Registration Index, 1837-2005," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:2DHG-KH5 : 13 December 2014), Benjamin Fletcher Smith and Mary Ann Knight, Sep Qtr 1845; from "England & Wales Marriages, 1837-2005," database, findmypast (http://www.findmypast.com : 2012); citing 1845, quarter 3, vol. 16, p. 277, Atherstone, Warwickshire, England, General Register Office, Southport, England.
"Australia, Victoria, Inward Passenger Lists, 1839-1923", database, FamilySearch (https://familysearch.org/ark:/61903/1:1:QPHC-TF3J : 15 October 2019), Benjamin F Smith, 9 Apr 1856. Ship Mooresfort, Benjamin F Smith, occupation Hatter, 32, traveling with Mary Ann Smith, 32, Thomas Smith, 10, George Smith, 6, and Clara Smith, 9 months.
"Family Notices" The Sydney Mail and New South Wales Advertiser (NSW : 1871 - 1912) 19 April 1890: 893. (http://nla.gov.au/nla.news-article162071786 : accessed 3 Nov 2020). "Smith. - April 13, at Sydney, Benjamin Fletcher Smith, aged 65."
"Family Notices" The Argus (Melbourne, Vic. : 1848 - 1957) 16 April 1890: 1. (http://nla.gov.au/nla.news-article8600695 : accessed 3 Nov 2020). "Smith.- On the 13 inst., at Sydney, N.S.W., after a painful illness caused by an internal tumour, Benjamin Fletcher Smith, third son of the late Thomas Smith, currier, of Woodbridge, Suffolk, England, aged 65 years."