As I said in a comment on the previous version of this post seen here, the family tree issues are compounded by the issue of partners turning into siblings, that was reported at least a year ago and was never looked into more.
This is the third version of this thread in less than a month, that in itself is ridiculous at this point and needs to be addressed.
But yes, I have this issue as well as connections just being plain wrong. One example - I had a daughter-in-law sim became the actual daughter of my family founder; it was carnage!
The family tree is also affected by not being able to set parents of pre-existing sims (first brought up 11 months ago btw...) due to what has been referred to as 'phantom parents' - basically non existent invisible placeholders that destroy the family tree and ability to use CAS full edit mode in the intended capacity when editing relationships.
Which begs the question did the team look at the relationship data? or did they just think it was only a UI issue? Because I think it might be both mixed into one with the comments consensus and the mess that is the pictured example.
The frustration is exhausting, mods can't fix this, at least for the moment but it should not be up to mod creators to make the game fundamentally functional. I personally can't play my multi legacy save until this issue is fully resolved, the word 'unplayable' gets thrown around a lot, I've said it myself in the last version of this report. But for the purpose of legacy players who rely on the family tree this is pretty game breaking.
I can't speak for everyone else but the family tree, connections and relationships are major aspects of how I play, so until its fixed the sims 4 is just a building simulator for me.