Ellen,
Isaac Stewart’s townland will be Lisrodden. Agnes will be Moboy. (Spelling varies though).
Here’s daughter Agnes birth on 13.3.1865, which shows the mother Agnes (Nancy) was still alive then. Nancy/Ann/Agnes are all interchangeable in Ireland (and Scotland) in case you didn’t know that.
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1865/03588/2322612.pdf
They also had an un-named female born on 1.6.1868 when they were living at Killyless:
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1868/03444/2264390.pdf
Statutory birth registration only started in Ireland in 1864 so for any children born between 1853 and 31.12.1863, you would need to rely on church baptism records which, given they were Presbyterian, may not be available on-line. Do you know which church they attended? The burial information you have found suggests Portglenone 2ndPresbyterian, but people weren’t always buried in the churchyard of the church they attended and so that may not be correct. (Portglenone 1st has no graveyard so its congregation must use other churchyards, for example).
Here’s Mary Stewart’s birth on 4.3.1881 at Moboy which reveals her mother’s maiden name was McLeister. In at least one of the births it is McCleister. Same difference, and presumably a variation of McAllister.
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1881/02844/2042230.pdf
I see other children to that couple as follows:
Catherine 22.6.1869
William 16.2.1871
James 15.10.1872
Jane 7.2.1875
John 16.6.1877
Elizabeth 18.8.1878
Catherine’s birth here:
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1869/03387/2241686.pdf
So Agnes Stewart must have died between June 1868 and June 1869, and likewise Isaac must have remarried within that period too. Indeed since there is only a 12 month gap between the last child by Agnes and the first by Margaret, he must have been fairly quick off the mark in finding, courting and marrying his new bride.
I have searched for Agnes/Nancy’s death and for Isaac’s remarriage but cannot find either in the statutory records. There were only 6 female Stewart/Stuart deaths in 1868/9 in the Ballymena area. Most were too young or old to be of child bearing age, and none were named Nancy or Agnes. So her death is a mystery. Likewise the remarriage. No sign of that anywhere in Ireland.
Found this probate abstract on the PRONI wills site. William died intestate. The probate file itself is in PRONI in paper format. (They’ll copy it for a fee, if you can’t get there in person). The original administrator failed or was unable to carry out their duties and so a new administrator was appointed in 1945. So that file may tell you who was still alive at that time.
Administration of the Estate of William Stewart late of Moboy, Co. Antrim, Farmer, who died 25 April 1920, granted at Belfast 6 October 1920 to John Stewart, Farmer, the Curator or Guardian of the children of the deceased. Effects: £585 8s 0d.
Stewart William of Moboy Portglenone county Antrim farmer died 25 April 1920 Administration (d.b.n.) Belfast 26 September to Charles Stewart farmer. Unadministered effects £119 15s. Former Grant Belfast 6 October 1920.
William’s death here, aged 49. His wife had pre-deceased him and the informant was his brother John:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1920/05125/4410591.pdf
Ballymena Observer 9.10.1936 has a warning notice from John Stewart of Lisnahuncheon and Maboy about trespassers with dogs and guns. So sounds as though he had 2 farms.
PRONI has these 2 abstract, plus the wills themselves are on-line, on the PRONI site:
Probate of the Will of David Stewart late of Maboy County Antrim Farmer who died 16 September 1897 granted at Belfast to James Wilkinson Farmer and Robert S.Kilpatrick School Teacher both of Maboy.
Probate of the Will of Margaret Jane Stewart late of Maboy County Antrim Widow who died 18 March 1900 granted at Belfast to James Wilkinson Carpenter.
This ties in with this stone in Townhill:
Erected in loving memory of David Stewart, Maboy, who died 16th Sept 1897, aged 70 years and his daughter Mary, who died in infancy. Also his wife Margaret Jane, who died 18th March 1900, aged 60 years.
Townhill graveyard is the graveyard for Portglenone 2nd Presbyterian church. It closed around 1910 and the building itself is long demolished. However it’s records survive in PRONI. Baptisms from 1821 and marriages from 1822.
Possible marriages for some of Isaac’s children (I only looked up to 1915):
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1887/10799/5938291.pdf
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1903/10220/5720267.pdf
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1910/09971/5625454.pdf
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_re…