Thanks for the reply, Josiah. I'm not familiar with that kin filter plugin; I'll check it out. I'm really more keen on something that will draw a nice diagram than on a filter that helps me query children (since Tidgraph can walk a whole tree of related tiddlers as well).
It appears Tidgraph is semi-abandoned in that the code for it in Github appears to be a couple versions behind (e.g., it doesn't have the custom modes mentioned at its documentation site) and when you import it, it's unfortunately obfuscated JavaScript, which is quite painful to work with.
Nevertheless, I've hacked the obfuscated JavaScript for the plugin to make the custom mode argument pass in the first part of the filter I need (children who list the current node as "father") and the filter argument receive in the second part of my filter (append in all children who list the current node as "mother").
So I don't have spouses (a shame, but I can manage for now without this), but my hacked Tidgraph will now find and draw all descendants (both from male and female lines) given a starting tiddler (a top-level parent).
For those interested in this (note: it may break your wiki / Tidgraph), you have to find and change the following section (the obfuscated JavaScript is all jammed on a single line, so line numbers are not helpful here) in $:/plugins/ihm/tidgraph/utils.js:
default:b="[["+a+"]"+c.mode+"]+"+c.filter}
to:
default:b="[["+a+"]"+c.mode+"] [["+a+"]"+c.filter+"]"}
After this change you have to save utils.js and hard refresh / reload your TW. Then you invoke it like this (using my previous example):
<$tidgraph start="James" mode="listed[father]" filter="listed[mother]" layout="S"/>
Which will now generate the needed OR style filter (and draw a full lineage).
[[James]listed[father]] [[James]listed[mother]]
Woot!