Our Children
From my (Bo) perspective generation 4 is that of my children, and the other children of generation 3. Chronologically they would start with Maria.
Children are linked to from their biological parents so that, when there are divorces the issue of the first marriage are shown under each of the divorcees… the existing children of a new spouse are listed under their biological parents.
This is just a way of making the site and relationships relatively easy to negotiate even although us step-parents consider our children to be a collective rather than just a biological issue.