Relative confusion

Yes, great grandfather, grandson, and great grandson would generally be considered relatives of an individual in the context of income tax. This is because they are all lineal ascendants or descendants of the individual, as they are all related in an ascending or descending line.

A lineal ascendant is a person who is related to the taxpayer in an ascending line, such as a parent or grandparent. A lineal descendant is a person who is related to the taxpayer in a descending line, such as a child or grandchild.