Valentine had children Martha and Joseph born elsewhere and of the right age, which had me thinking they were involved. The problem of referring to Joseph and Samuel Edmund as boarders was an issue- were they close relatives or family? That Valentine did not mention Martha in his will could be explained by her being married. I am still struggling with my computer to get into PRONI wills, but yesterday saw that Alexander and then Samuel were offered property if they would return to live in the home.
However, Martha McCutcheon having father Joseph sounds right given her son's name and is very valuable.
Samuel Edmond who went to Canada to his sister is the man born a year before in 1881. He is on Rootsweb, son of Samuel and Martha (Maxwell) Doak and marrying twice in Belfast. He is Samuel one place and Edmond another. Samuel, the father, has parents Alexander and Jane. Dau Martha married James Anderson and lived in Gilford. The close naming in the families is amazing as Edmond was rarely used. I am hoping to find why it exists, the name and the relationship.
The Sarah who lives with Elizabeth in 1901 seems to be Sarah, the mother of Alexander, Sam Edmond, etc. At least that Elizabeth looks the same age as the one born in 1884 per her NY obituary. She is listed as female in the civil records I think. I can probably order that as well as Samuel Edmund's. Only the 1882 birth record for Samuel Edmond is definitely a record for this family which would give Sarah's last name.
Sarah is about 50 (Doak dates are often off) and would have married about 1870 and the birthyear of the oldest child I know is 1875. If Sarah is 50, that puts the date of father Joseph's marriage close to or before 1850 which means it is not in civil records. However, Sarah's marriage should be and she might be using a middle name. Her husband, if dead, would have died between 1883 and 1901 and also may be using his middle name. I haven't checked that out.
I have a list of local Doak marriages, but didn't track ones like Valentine's who was moving around. I have looked for Joseph/Sarah marriages elsewhere in Ireland, but not found anything.