The birth of only 3 Watsons in a tight poriod in Clonsast would point to William, Henry and John being brothers.
1846 There is a marriage of a John Watson of Clonsast on 8 Oct 1846 (the cert could be got from state records) in Clonsast, to Elizabeth Acrett at Clonsast. I suspect that is the marriage in question. Edenderry vol 5 p625
1853 Griffiths in 1853 has a John Watson farming at Kilcloncorkry, with 47 acres and a house.
1884 The Sarah Ann Waston who marries James Grant in Feb 1884 in Dublin (James is a brother of Thomas Grant who married Marie Watson), then emigrated to Brisbane, Australia in 1884, has a father John Watson. Her death cert states she was born in Kildare, and does not give her mother. A witness at her wedding is Martha Watson, making her probably a sister.
It is just a guess that the chart is as above, given the marriages to Thomas and James Grant