Yenram in Australia,
Did you ever find more about your ancestor Samuel Tibby? There's a Samuel Tibby in Killeevan parish in the Tithe Applotments, 1825. Possibly father or other older relative of your Samuel born about 1817?
I'd suggest searching Church of Ireland as well as Presbyterian records. I saw Tibby entries in the Killeevan Church of Ireland registers in County Monaghan a few years ago, but wasn't researching that family myself, so only copied a Tibby where there was an intermarriage with my lines.
Jane Tibby married Newbliss blacksmith Thomas Wilkin before 1834; they baptised children (Mary 1834, Joseph 1837, William 1839) in Killeevan Church of Ireland. The Wilkins are my cousins.
Killeevan is an old old church. The current building dates to 1858, but the register goes back to 1811. Then Newbliss Church of Ireland records begin in 1841 -- another possiblity to search.
Newbliss Presbyterian records might show Tibbys of interest, even though it's marriages 1845+ and baptisms 1856+, and your Samuel Tibby seems to have married before 1841. I'd search all the Tibby marriages in Newbliss, since the entries will have the couple's residences and fathers' names. I'd search baptisms for Tibby children, as well. Also, you can find Tibby marriages in civil registrations (1845+) and check for residences and fathers' names. Just might connect the dots on an extended family that way.
All of this is dependent on your having an Irish-resident friend/kind volunteer/professional researcher search the Co. Monaghan church records on microfilm at PRONI, or original books in ministers' custody and at the RCB Library in Dublin, since you're in Australia.
Best of luck, and you're welcome to write me directly (private message to exchange email addresses) if you'd like more help.
Annie