Margaret Tobin, born to James Tobin and Margaret Ahern, was baptized on 06 June 1851, at the Clogheen Parish Church in South County Tipperary, with John Tobin and Ellen Lonergan as sponsors/godparents. A copy of the original baptismal certificate can be found at https://registers.nli.ie/parishes/0116
Variants forms of the parish name are: Ballysheehan, Shanrahan and Ballyporeen. In a later document from Griffith’s Valuation around 1852, you will see that James Tobin farmed land in Shanrahan.
I found records for two other siblings, Mary Tobin and John Tobin.
Mary Tobin was baptized on 27 Nov 1845 at the Clogheen Parish Church with Thomas Burk and Mary Tobin as sponsors/godparents. A copy of the original baptismal certificate can be found at https://registers.nli.ie/parishes/0116
John Tobin was baptized on 20 Jul 1848 at the Clogheen Parish with Michael Kenely and Johanna Tobin as sponsors/godparents. Also see
https://registers.nli.ie/parishes/0116
You mentioned a sister Johanna Tobin but I was unable to find documentation on her, and there probably were other children of James Tobin and Margaret Ahern but I could not find back-up documentation.
James Tobin and Margaret Ahern were married at Ballylooby Parish on 19 Feb 1844 at the Ballylooby and Duhill Church. Patrick Sullivan and Mary Going were witnesses and Father Michael Power was the officiant. A copy of the original marriage document can be found at:
https://registers.nli.ie/registers/vtls000632123#page/1/mode/1up
Griffith’s Valuation of around 1852 lists James Tobin in Shanrahan as a farmer renting 19 acres of land and a house. William Ahern rented the adjacent land and also had 14 additional acres of land and a house nearby. William Ahern may have been related to Margaret Ahern, Margaret Tobin’s mother.
I hope this fills in some blanks for you. If you need to contact me please email. My address is robanglin@aol.com
Good luck!
Rob Anglin