On the 1881 census you refer to Joseph is 48 and Eliza 38 both born Ireland.
There are 9 children listed as well. 7 born in Scotland 2 in England.
That is the family of Joseph Campbell and Eliza(beth) Clegg whose children included
Jane, born 1864 in New Monkland
Joseph Alexander, born 6 June 1872 in New Monkland
David, born 4 March 1874 in New Monkland
Elizabeth, born 1876 in Lanchester
Margaret, born 1878 in New Monkland
Sarah, born 2 January 1881 in New Monkland
So if you are sure that your Eliza's maiden name was Heathwood, this family is not the right one.
In the indexes to Scottish statutory records of births, marriages and deaths there are no births of a Campbell with mother's maiden surname Heathwood, no marriages of a Campbell to a Heathwood, no deaths of a Campbell with mother's maiden surname Heathwood, and no deaths of a Campbell with other surname Heathwood. This doesn't exclude the possibility that there were births or deaths where the mother's maiden surname has yet to be added to the index, but most births before 1900 do have the mother's maiden surname indexed.
So what do you definitely know for certain about your Joseph Campbell's family?