Question about about Scandinavian elective succession.

So this is post number 5683 this week about succession, I'm sure but I've come across a situation I don't quite understand:

I started a game as the default chieftain of angermanland which is in Sweden and worked my way up to king of Denmark. I'm still tribal and I have just reformed the asatru faith which is the first time I've done this.

Through a series of invasions and subjugation wars, I currently control most of Norway and Finland via my vassals (Norway is currently held by a Christian king of Sweden so I can't get the title without a war) and Finland hasn't been created yet.

My main duchy is in Denmark and I also hold another duchy in Denmark.

I have confederate partition and equal succession. Denmark has Scandinavian elective succession.

I have 3 living children: A (oldest daughter) B (oldest son) and C (younger daughter who is in a patrilinial marriage to one of my vassals).

Under Scandinavian elective, I can nominate a distant relative so I nominated a niece of mine for her good stats and because she's young.

Because I have confederate partition, I am thinking that my two duchies will be split between my three children somehow and niece who is nominated as queen gets nothing.. or at least that's how I thought it would work but for some reason, currently my niece who stands to inherit the kingdom title also gets everything else. I lose nothing to my other children.

I have no idea how that happened. Did I break the game?

I may have removed my oldest son from the succession because I gave him Jorvik which he was going to inherit but this was before I reformed the faith and added equal succession rights.

My laws automatically were set to equal but it has removed my actual children from the succession entirely.

My game is unmodded save for some quality of life stuff (knight manager and extended outliner).

Am I missing something terribly obvious here?