So I found this picture on the deep dark internet and I instantly became excited.
It suggests there is a mod or another possibility out there that can make our Sims 3 familytrees larger?!

Do any of you know it? where to find it? Or was this photoshopped or somehow edited..

I play massive families so I would really love it if it were real! Again, this picture is not mine - I blatantly robbed from the web

I know you can set the levels to more than 4 with NRAAS MC/Cheats. NRAAS->Settings->Family Tree Levels and put in the value you want.
I noticed tho' that with 15 children or more, the family tree fails to show at all.
My Grandfather was in a family with 15 children.

I can't quite reach a screenshot right now, but one of my sims in an earlier generation had...I think it was 23 illegitimate children in addition to his 4 (more or less, don't ask) legitimate ones. They all show on the family tree. But I were to increase the number of levels to display beyond 4 or 5, I do expect it will fall apart eventually. Strange how we seem to get different points of collapse on that one.