I love family trees: they're interesting, complex, data-driven, and beautiful. There are some very challenging decisions you need to make to make a tree readable, like whose ancestors to show, whose children, and how far back. To give you a sense, I have ~3,500 people in my family tree. I want different trees to show, say: a) all descendants of a root ancestor, or b) all of my ancestors.

This is reasonably easy to use and build out a simple tree. Here are two opportunities:

1) There are some UI areas that aren't totally intuitive (e.g., double click to add name), and generally it feels to "clicky" (e.g., too many clicks to get to the action I want). I think your goal is super-simple and "delightful" vs. full-featured.

2) The 1:1 relationship lines get complex, as every parent is linked to every child (so you end up with 2n lines that all overlap).