Here’s a copy of the marriage certificate:
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1857/09540/5458436.pdf
At the time of their marriage, George & Eliza were living in Tirmegan which is a townland a couple of miles north of Newtownstewart. Neither family is listed in Tirmegan in Griffiths Valuation of 1858. Labourers often moved around a lot to follow the available work and can be hard to trace.
http://www.askaboutireland.ie/griffith-valuation/index.xml?action=nameSearch
Here’s the birth of an un-named son at Bunderg in 1865:
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1865/03563/2312405.pdf
Here’s the birth of an un-named daughter on 23.7.1867 (possibly Mary Jane who died in Alberta in 1967 according to trees on Ancestry).
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1867/03475/2276731.pdf
I can also see births for Lily on 18.6.1869; Matilda 30.4.1871, Andrew 10.3.1873 and another un-named female on 17.2.1875. There may well also have been children born 1857 – 1863 but birth registration hadn’t started in Ireland then and so you won’t find any birth certificates. Some trees on Ancestry record an Elizabeth b 1864 who died in Saskatchewan in 1931. I don't see a birth for her so she was probably born in 1863 or earlier.
The last born child only lived 2 hours. Death here:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1875/020634/7239464.pdf
Eliza died the following day and her death is on the same page. Informant for both deaths was a Lilly McFarland of Sion. Presumably a close relative. This is the only Lilly McFarland who might fit, in the 1901 census. Although living in Belfast in 1901, I note she was from Tyrone:
http://www.census.nationalarchives.ie/pages/1901/Antrim/Falls_Ward/Cave…
This is the only death I can see for George Semple that might fit:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1900/05771/4631338.pdf
I think it probably is correct because the informant was Charles Higney and I see his wife was named Matilda (George's daughter). Here’s the family in the 1901 census:
http://www.census.nationalarchives.ie/pages/1901/Tyrone/Camus/Bearney_Glebe/1753743/
Here’s their marriage:
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1899/10370/5775718.pdf
BonnieAnn Hill has a tree on Ancestry that says Eliza McFarland’s father John lived 1798 – 1882 and died in Omagh. There is a death that matches those dates but the John there was a Gentleman (ie lived on private means) and not a labourer and so I would doubt it’s the right John, as her father was a labourer. Here’s the death anyway:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1882/06403/4838704.pdf
Here’s a likely marriage for Andrew Semple in 1899. His address was Bearney which is evidently where the family had been living. One of the witnesses was Charles Higney (witness to George’s death):
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1899/10398/5786150.pdf
Here’s Kate and daughter in the 1901 census:
http://www.census.nationalarchives.ie/pages/1901/Tyrone/Camus/Bearney_G…
Here’s the family in the 1911 census:
http://www.census.nationalarchives.ie/pages/1911/Tyrone/Douglasburn/Drumnahoe/848124/
Daughter Lily was born in Scotland so the family had evidently been living there for a while. (Folk from the north of Ireland often went to Scotland for work).