If I am understanding your question correctly, the design of Genogram sample and the GenogramLayout requires that every person have either zero or two parents. When there are two parents, there is a “marriage” link between the two parents and that link has a label node which is the Link.fromNode of each link that goes to each child node.
So it is not possible to have a person node that has exactly one parent node. Both the mother and the father nodes must be present and linked with each other.
Now that doesn’t mean both parent nodes need to be shown – you can certainly make one spouse node be unseen by making its opacity zero. This is actually done in commented-out code in the samples/genogram.html sample, at the end of the setupDiagram function.