A Family Tree at Ancestry titled McMurray Family Tree has Margaret married to a Donald McTavish and they had about 8 children. According to the 1891 and 1901 they were living in East Bruce, Greenock Twp. I have not been able to find a marriage or death record for either Margaret or Donald and to really make sure this is correct.
According to this family tree Margaret and Donald had: Matilda, Annie, Christina, Alexander, Henery B. and Nellie.
This is the link to the Ancestry.com family tree titled McMurray Family Tree which you may need a membership to see or use your library card at the library to access the library version: http://person.ancestry.com/tree/9807004/person/-497599555/facts
My records show that Margaret was born 6 November, 1854 in Rawdon, Hastings Co., Ontario and that she died in Kingston. So I found as follows, another Margaret going by the name Bella Margaret who appears as a dressmaker living in Kingston, Ontario at the Rockwell Hospital. I had in my notes that she was living in Kingston. This does not list her parents names unfortunately. Rockwell might have records that could be studied for more clues.
Death, Brown, #013868, Bella Margaret, Rockwood Hospital, KIngston, Ontario. Female, White, Single, age 71, born Hastings Co., birthdate unknown, dressmaker, was in Kingston 18 years and life in Ontario name of father and mother unknown, Dr. Ryan, Lockwood Hospital, Kingston, date of death October 22, 1924, she died of pneumonia, with arterio sclerosis for several years. Recorded October 24, 1924. Source: Ontario, Canada, Deaths 1869-1938.
There is a Bella Brown who is a patient at the Rockwood Hospital in the 1921 Canadian Census, she is listed as 68 years old with birth about 1853 in Ontario. This Bella is also listed there in the 1911 Canadian Census.
The above Family Tree using the census and my search using a death record and more census does in no way prove that this is the correct Margaret Brown. Definitely more research will need to be done. The OCFA has several Margaret McTavish’s passing in Bruce but this is only and index and more searching would need to be done.
As for the sister Harriett, I have not been able to find anything further on her at all. Her mother would have been 41 years old or older if this Harriet was born in 1860.