Hi. My great grandfather is James Sanderson, born Ft. Garry, Manitoba in 15-jul-1861. His father was William James Sanderson, born 14-feb-1830 and married a Mary McNab (father John McNab). Most of the children were born in Ft. Garry, Popular Point or Muddy Flats, Manitoba. I have most of the names of the children that you have except for Isabella and Samuel and I have Marianne, Nancy and Thomas although I'm thinking that some of the names maybe middle names.
I believe that William James' father was also called William and he resided in Canada. He died the 6-dec-1836. He was married to Margaret Cook who died 27-jul-1827 and re-married to Jane Badger who died 27-jun-1831. It is thought that his only son, William, was raised by relatives although I have not been able to verify this.
There is also information (and I have not been able to verify this) that a James Sandison, born 1756 or 1776; died 1820 or 1825 was married to Nancy Cree Indian, born 1779 or 1780 and died 1849 or 1851. They had at least three children, William Sanderson, Robert Sandison, born 1795 and James Sandison, born 13-jan 1826.
Unfortunately, I have only been searching the Internet for Sanderson information for the past couple of months and therefore have not been able to verify some of the information. This weekend I am attending a Sanderson Family Reunion in Springside, Saskatchewan. Hopefully I can verify some of the information there.
Should you have some birthdate for William James Sanderson's children I would be grateful to receive them. I have birthyears for most of them but I only have five actual birthdates.
I hope this helps you continue on with your search.