In a first-marriage nuclear family, the members include the biological parents and their blood-related dependent children. In the case of remarriage, the new household will not be complete as it stands, for there will be a family member living outside it (the other biological parent) who must be included within the overall system. Therefore, there will be need to be a “boundary with a hole in it” to offer this parent easy access. This unclosed boundary can be fraught with difficulties.

The new...