The Family Tree is one of the more easily 'broken' parts of the game.

Here's the results of less than ten minutes' banging on the CAS engine:

I (accidentally) made a polygamous family (two husbands, three wives, all of whom were, according to the engine, related); when I added a child to the mix, after a bit more nudging, it became the biological child of all three 'wives' and both 'husbands'.

Throwing caution to the wind in an attempt to see how far I could go in my experiments, I attempted to add another 'husband' to the mix, but three wives and two husbands appears to be the upper limit for mutated pseduo-families.

The 'family' I created was accepted by the engine, and was perfectly functional when I finally loaded them into the game (ie, all interactions were intact and I could see no visible bugs or glitches).  However, *before* I loaded them up, the Family Tree had a bit of a seizure. 

Apparently, it wasn't tested thoroughly enough by People who Think Like Me (ie, the kind of person that will go into an adventure game and try taking 150 napkins when you'll only ever need one and a napkin has no real use in the game anyhow). 

The Family Tree choked after a bit more fiddling, first by taking away everyone but the parents and one of the non-related children, and then seizing up totally and leaving only one parent, one child, and an ellipsis (which is the '...' used to indicate extended relations) and totally refusing to ackknowledge any further alterations to their Family Ties.

I couldn't see any other family members, nor could I change any relations, but the game was still fully functional and all members of the family were present and recognized by the game engine when the family was loaded into the game.

If you push it any farther, you'll end up with a blank Family Tree window.

As a note, I'm not really certain how I did it in the first place -- all I know is that if you change the family's name at the Family Tree screen, and then go back and fiddle with the family member's last names, you'll eventually break the engine if you do it often enough and in enough variations.