Finally found the family in the 1851 Liverpool, Lancashire, England census (mis-enumerated surname as ESTHAN, instead of HESTON, you can hear the similarity when you say it. The family name changed to HASTINGS in most documents I have), which helps triangulate the family members, births and movement.
Here's what I know now:
Michael HESTON (went to HASTINGS eventually) married Bridget STUART (went to STEWART for her brother and descendants)
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Westport Marriages, Diocese Tuam, Parish: Aughaval (Westport)
Sept 8th, 1826
Mich'l HESTIN to Bridget STUART
sp: Daniel HESTN and Anne LYDON 1.0.0
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The researcher said the Hastings surname was particularly strong around Drummin in Aughaval and Cushlough in Aghagower, so that's my assumption (and that Bridget was in Aughaval as the bride's parish where the marriage took place). I finally located this on the map just due south of Westport off N59.
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Known children with ages:
>Edward HASTINGS b: Abt. 1831 in Ireland d: Bet. Jan - Mar 1873 in Liverpool, Manchester, England
(Married in Liverpool in 1851 to Ellen REYNOLDS, had 8 children who may have stayed in Liverpool. Note there was another Edward HASTINGS from County Mayo who married a Bridget in Liverpool that may be kin)
>Anna Bridget HASTINGS b: 12 May 1837 in Westport, County Mayo, Ireland d: 23 Sep 1931 in Topeka, Shawnee, Kansas (5-9-1931?) - She immigrated to New Orleans in Feb 1855
>James HASTINGS b: Abt. 1837 in Ireland (he imm. to New Orleans with Mom, and 2 sisters in April 1855, but did not find him among the family after they landed in America)
>Thomas HASTINGS b: Abt. 1838 in County Mayo, Ireland d: 06 Nov 1867 in Lexington, Lafayette Co, MO (unknown Imm., but most likely with father and younger brother Peter)
>Sarah HASTINGS b: 20 Jul 1843 in Westport? (wag), County Mayo, Ireland d: 25 Aug 1923 in Kansas City, Jackson, Missouri (imm with Mother, brother, and sister)
>Peter HASTINGS b: Abt. 1845 in Ireland, (not much known about Peter, other than the one census, and a reference in one legal document in Missouri tying him to his Father)
>Margaret Mary HASTINGS b: 27 May 1849 in Liverpool, Lancashire, England d: 28 Aug 1912 in Kansas City, Jackson County, Missouri (imm with Mother, brother, and sister).
Any help on the HESTIN/HESTON/HASTINGS line from County Mayo in the 1800s would be appreciated.