A friend in Dublin recently looked up the Tithes Index of 1834 and found that there was only one Magiveran (McGivern) family living in Greencastle - so it is almost definitely my family and the name of the head of household was Thomas. This suggests that Thomas was Daniel's father.
The will of Daniel Magivern (McGivern) dated 1851 leaves the farm to be equally divided between his 2 eldest sons, Thomas and Daniel. He then goes on to mention his 3 daughters Mary, Cecily and Biddy and his 3rd son John (my great grandfather). Neither Thomas nor Daniel could have had children at that time as he states that should they "die without heirs" then John was to "fall into their shares and liabilities". Daniel's will also mentions his wife Mary, who we beleive was his 2nd wife and his brother Philip in America.
John McGivern (b.1840) married Maria Cunningham/Cunnyngham (unsure of spelling)(b.1852?) and they had 11 children, Sarrah Anne, Daniel, Thomas, Wilfred, Henry, Matthew, Nicholas, Henryetta, John, Maisie and Phillip.
Nicholas (b.1891) was my grandfather and he married Mary Catherine Cull (b. 1898).