Hi, SussanahinOZ, I see Charles and Margaret on the 1901 census as boarders in the house of Richard Longsden and his wife Mary Agnes. This couple have a 10 month old son Thomas and a stepson named Joseph Macdonald. Reference: Piece 3785, Folio, 104, Page 25.
There is a marriage for a Mary Agnes Macdonald and Richard Longsden in the December quarter of 1899, Ashton, Reference: 8d 785. So, it seems that Joseph is a child of Mary Agnes, pre marriage to Richard. It is possible that Mary Agnes and Margaret are related, possibly sisters?
If they are, this further supports the findings of Heatherjulie in that Margaret's maiden name was Macdonald or McDonald.
Modified: On further examination it appears that this Mary Agnes is in fact the daughter of Margaret Macdonald. I cannot find a marriage for Margaret and Charles. However, I suggest that you look at the 1911 census at the years married for this couple and the number of children of the marriage.
Regards
Kathb