Answer: Skip generation family
Explanation:
Skip generation family is the family that have grandparents and grandchildren without the layer of parents and thus, a generation is skipped in the family. In this structure of family, grandparents take care of grandchildren and raise them.They are also regarded as grand-families.
According to the question, Joseph and Roxanne are the grandparents and are raising their grandchildren without the presence and assistance of their parents. Thus they can be considered as skip generation family.