The 1901 census shows the Fox family farming in Teebane West, in Co. Tyrone. They had 5 children living at home.
http://www.census.nationalarchives.ie/pages/1901/Tyrone/Crockanboy/Teebane__West/1744323/
Here’s Patrick Fox’s marriage in 1878. His wife’s maiden name was Fox and she also came from Teebane so was [perhaps a cousin.
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1878/11109/8066088.pdf
An Arthur Fox was one of the witnesses.
Some probate abstracts from the PRONI wills site:
The Will of Patrick Fox late of Teebane West County Tyrone Farmer who died 19 July 1892 at same place was proved at Londonderry by James M'Namee of Crockanbuoy in said County Farmer the sole Executor.
Above will is on-line on the PRONI site and mentions son Arthur and daughter Ann.
Administration of the estate of Patrick Fox late of Teebane West Seskinshule County Tyrone Farmer who died 25 December 1905 at Omagh granted at Londonderry to Margaret Fox the Widow.
Fox John of Teebane West Drumlea Omagh county Tyrone farmer died 21 September 1921 Administration Londonderry 8 May to Mary Fox the widow. Effects £20.
Fox Michael of Teebane West Gortin county Tyrone farmer died 15 August 1935 Probate Londonderry 11 August to Denis Fox farmer. Effects £33 16s.
Fox Arthur of Teebane West county Tyrone farmer died 21 June 1936 Administration Londonderry 19 April to Rose T. Carolan married woman. Effects £55.
Fox Bernard of Teebane West Drumlea Omagh county Tyrone farmer died 8 April 1948 Administration Londonderry 11 February to Patrick Joseph Fox farmer. Effects £349 5s.
Fox Bridget of Teebane West Gortin county Tyrone widow died 12 December 1947 Probate Londonderry 27 April to John Fox farmer and Rose Teresa Carolan married woman. Effects £5146 13s. 4d.
Fox Mary of Teebane West Omagh county Tyrone widow died 12 February 1951 Probate Londonderry 30 November to Annie Fox spinster. Effects £60.
Fox, Peter of Teebane West Drumlea Omagh county Tyrone farmer died 15 January 1962 at Tyrone County Hospital Omagh aforesaid Administration Londonderry 22 March to Bridget Fox the widow. Effects £939 13s.
Fox, Bridget of Teebane West Drumlea Omagh county Tyrone spinster died 28 January 1967 at Tyrone County Hospital Omagh county Tyrone Administration Londonderry 25 October to Annie Fox spinster. Effects £25.
The relevant Probate files should be held in PRONI in Belfast.
There were 6 Fox households in Teebane West in 1911, a total of 33 people, all engaged in farming. You’ll need to piece the various families together:
http://www.census.nationalarchives.ie/pages/1911/Tyrone/Crockanboy/Teebane_West/
According to the 1911 census Patrick & Mgt Fox had 7 children all of whom were still alive then. The births appear to be:
Catherine 9.9.1879
Patrick 4.4.1882
Anne 20.10.1884
Isabella 30.12.1887
Francis 20.1.1891
Margaret 27.12.1893
Mary 14.7.1898
You said you thought Margaret was born 29.3.1888. That doesn’t appear to be the case. Her birth was in 1893, according to her birth certificate.
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1894/02272/1853636.pdf
Looking at the Valuation Revision records on the PRONI site, Patrick & Margaret’s farm then was plot 13 which was 20 acres. They owned the freehold having bought it under the Land Act ie with a Govt mortgage. That farm today is near An Teach Bann B & B. 345 Crockanboy Rd.