I would agree on the family names as often children took on as forenames their mother's maiden name as well as handing down names. Its also possible there was a Duke in the family at one time and the family liked it as a first name.
You can look up Peerage-Ireland, Debretts and other such like websites.
You could try googling Registry of Deeds-Ireland
as this is where you might find records of land, mortgages, marriage settlements etc. Look for freepages.genealogy.rootsweb etc. you can search by family name. I'm not going to type them out but the name Meredith and Ferguson are listed.
there as gentlemen and esquires, some for Dublin but keep in mind these folks would have homes in Dublin for the
social season as well as their properties in the counties.
Military records - follow the link on the website for
the National Archives, Kew, London - now records are on a pay website.
MILGENIRE, Military Genealogy Ireland, a sharing board for
A website for RC baptisms for Sligo and Ballysadre/Kilvarnet
is showing baptisms from 1842-1899 and marriages from 1858.
Church of Ireland (as most of those who own land were) has only 1 parish of 25 in Sligo with records from 1762 (Emlefad & Kilmorgan) the remainder after 1800. Also Ballisodare (as spelled) has no Church of Ireland records.
This could mean there are few records for Ballisodare or that the Foundation has never collected these for their database. You can contact the Representative Library of the Church of Ireland in Dublin, they are online, and look for their parish records. Over 1/2 of the CofI records in Ireland were burned in the 1922 Four Courts fires.
A website that can tell you from the Griffith Valuation where you will find the surnames Ferguson and Meredith, one of the counties listed was Sligo. The others, Armargh, Belfast, Cork, Down, Dublin/Dublin City.
Good luck in your search, Ireland is difficult at best.