Welcome to Ireland Reaching Out!
I do have a few comments but I wanted to let you know that I live in the USA.
First, on Roots Ireland I found a transcription of an 1840 baptismal record for a Mary Hamilton in the Castlerea RC church. Is this the Mary Hamilton in your message born around 1835? See below.
Second, I believe the townland for Joshua Hamilton is Cloonslanor rather than Corslanor. Cloonslanor is located in Cloonfinlough civil parish and would be three kilometers southwest of Strokestown. I checked the 1855 Griffiths Valuation head of household listing for Cloonfinlough civil parish and there was a Thomas Hamilton listed in Cloonslanor. Possibly a son or brother to Joshua? See link below.
I located a civil death index record for Joshua in 1864 (as you indicated). Civil death record images are available starting in 1878 but the death records going back to 1864 should be online in the next year (we hope!). The informant slisted Joshua's age as 84.
Finally, the last two links are from the 1901 and 1911 censuses for Cloonslanor. The 1901 record shows a Margaret Hamilton, widow, with three unmarried adult children. The 1911 record only shows Patrick Hamilton. Margaret had died in 1902 (seventh record on page). https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_retur...
Let me know if you have any questions.
Name:Mary HamiltonDate of Birth:
Date of Baptism:06-Dec-1840Address:Not RecordedParish/District:CASTLEREAGender:FemaleCountyCo. Roscommon
Father:John HamiltonMother:Elizabeth MahonOccupation:
Sponsor 1 /
Informant 1:Patrick McLaughun Sponsor 2 /
Informant 2:Brigid Feeny
Group Registration IDN/RSR District/Reg AreaStrokestownDeceased Age at Death84Returns Year1864Returns Quarter2Returns Volume No8Returns Page No260