I already have the three children listed as step-children of the step-father and bio-mother but would like to show them as children of the two bio-parents also (which is not conventional).
Now I think I understand better, Judy. You set the children as Primary to the step-father and bio-mother, right? (Always check whether the relationship is Primary from the child's Detail view,, i.e. who are the two parents in the top slots. Checking from the parents Detail view doesn't help. The asterisk in the parent's view means something else.) That explanation makes things clearer. Actually what you are doing is "backwards" to what TMG expects. Doesn't mean what you are doing is "wrong", only that you are now battling TMG's automatic assumptions. Setting the "children of the two bio-parents" as Primary to both their bio-parents is what TMG expects and what all its reports assume. TMG "assumes" that Primary parent/child relationships are by definition biological relationships. Using the tag name variation of step-parent/child is intended to be only a visual aid to you. Just because you chose the Primary relationship type as step-parent/child, TMG will still treat it as a biological/genetic relationship because it is Primary. Any TMG ancestor/descendant linkages assume that Primary relationships are biological relationships. TMG expects that the user will use the non-bio relationship types only for non-Primary relationships, so automatically assumes any non-Primary relationship is not biological even if the tag type name is bio.
If you keep TMG's assumptions in mind, this is why TMG reports automatically list the Primary relationship children for parents in their Journal narrative, and do not list non-Primary relationship children. The name of the relationship tag is ignored, it is the Primary setting (from the point of view of the child) that matters to TMG.
Therefore, when you made the step-father and bio-mother relationships to these children Primary, these children will be listed automatically as the (assumed biological) children of this couple. Because you did not make their relationships to the bio-father Primary, they will not be listed automatically as his (assumed biological) children, even though you set the name of his relationship tag as bio. Only the two parents who are set as Primary for a child are assumed to be the couple who begat the child.
The purpose of the "trick" of using the NarrativeChildren tag is to be able to list children who are not Primary to either of the couple of interest, since non-Primary children are never automatically listed. TMG assumes that normally you set both the bio-father and bio-mother as Primary for their children. In that case you need the "trick" of adding text to the narrative heading of the "family" of the (non-Primary) step-father and (Primary) bio-mother so that the step-father's narrative could list these non-biological step children, since they would not automatically be listed for him as they are not Primary to him. In the bio-mother's narrative TMG assumes they will be listed as the family of the bio-father/bio-mother couple, as both are Primary for these children.
In your case, with the step-father and bio-mother set as Primary for these children they will automatically be listed in both of those people's narratives as that couple's family "as if" they were their biological children. The children will not be listed in the bio-father's narrative as he isn't Primary. And they will not be listed in the bio-mother's narrative as children of the bio-father/bio-mother couple since he isn't Primary. So now you have to do the "trick" for the bio-father and bio-mother family heading to get this couple's "family" to list these children, since they will not automatically be listed as they are not Primary for both of this couple.
Does that help explain what you are seeing any better?