Mardee, in case you are unfamiliar with place names in Ireland there are often many variations for the same townland which continues to the present day. One road near me has three road signs (one at either end and one in the middle at a junction) and all three signs use a different spelling.
These are the children of William and Margaret that I could find.
...
5. Henry Williamson 1886
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The minister at Banagher Presbyterian Church (from 1880 until his death in 1904) was Rev. William James Dalrymple Williamson originally from Aghadowey Parish. This
might be where the Henry's middle name came from.
These are the children of William and Margaret that I could find.
6. Catherine Ann 1887 Married 1911 James Alexander Smythe
7. Mary Eliza 1890 (Molly) Married 1914 John Taylor
12. George 1901
13. Margaret Rebecca Crawford 1902-1904
I am a bit suspicious about that last child Margaret. Her birth was registered my Mary (not Margaret or William) and her death registered by Catherine - I wonder if she was Mary's or Catherine's child?
No way of knowing. 
When the youngest child Margaret was born in 1902 her sister Catherine would have been about 15 and sister Mary about 12 so I'm doubtful either was the child's mother.
It's likely, given the mother's age and number of previous children, that it was merely Mary who went to register the new baby for her parents. It wasn't uncommon in those days.
Wee Margaret had bronchitis for 3 weeks before she died according to her death certificate (link posted earlier) and other children in the family or even the parents might also have been ill at the time. Certainly Margaret was likely tending to her youngest child and possibly exhausted by then.
