John & Margaret married in 1878:
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1878/11099/8062280.pdf
Griffiths Valuation for 1863 lists 3 Richard Robinsons in Wateresk. One on plot 5 in Wateresk. That was a 15 acre farm. There was also Richard Robinson senior on plot 43 which was 16 acres. Richard Robinson junior was on plot 38, a 19 acre farm. No easy way of identifying which of the 3 was John’s father. William Taylor (Margaret’s father) isn’t listed at that date.
One of the Richards died in 1874 aged 58:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1874/020647/7244746.pdf
His wife Catherine died in 1880. Samuel was the informant:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1880/06470/4861046.pdf
Samuel in 1901:
http://www.census.nationalarchives.ie/pages/1901/Down/Dundrum/Wateresk/…
Administration of the estate of Samuel Robinson late of Waterask (Wateresk), Dundrum, County Down, Farmer, who died 21 July 1903 granted at Belfast, to Mary Robinson, the Widow
Another Richard died in 1877 aged 51. Informant was Margaret:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1877/020542/7208356.pdf
This may be the widowed Margaret in 1901:
http://www.census.nationalarchives.ie/pages/1901/Down/Dundrum/Wateresk/…
According to the Jane Coburn tree on Ancestry the above Richard is your immediate line.
There was also a death in 1869 of one Richard aged 76 which is not on-line free yet. That may be the 3rd.
A widow. Apparently married to a Richard (presumably the 1869 death). She looks to be a close relation as her name appears as occupant of 2 of the farms in Wateresk in the Valuation records.
http://www.census.nationalarchives.ie/pages/1901/Down/Dundrum/Wateresk/1227050/
This looks to be your Margaret Taylor's family judging by the presence of grandson Richard Robinson in it:
http://www.census.nationalarchives.ie/pages/1901/Down/Dundrum/Wateresk/1227048/
Running through the 3 farms in Griffiths, the Valuation revision records on the PRONI site show plot 5 remaining in Richard’s name till 1881 when Samuel takes over. Plot 38 remains in another Richard’s name till 1873 when it goes to Ellen, then to Richard in 1875, then representatives of Richard in 1883, then Margaret in 1900. Plot 43 went from Richard to Ellen in 1875.
So it seems that Richard Robinson died in 1877, leaving John free to marry in 1878, but he didn’t stay on the Wateresk farm and instead acquired a farm of his own in Magherasaul. By 1895 he was back at Wateresk farming but by 1901 he was in Belfast. However his occupation then is still shown as farmer. There are no farms in that part of Belfast. Was he spending part of his time on the farm and part in Belfast?
http://www.census.nationalarchives.ie/pages/1901/Down/Victoria/Solway_S…