Not wanting kids, genetic?

Mostly posting because I'm bored and thinking of random interesting this. A childhood friend of mine just turned 26. She's the youngest of 6 siblings, 3 of which have a different father and were raised in a separate home. All her older siblings are in their 30's and 40's.

All 6 siblings are against having children, and 2 of them even got sterilized. She's been very adamant even since we were in elementary school that she never wants kids and that's been the case thus far.

I've never seen such a large group of siblings ALL be against children. (I'm not really a fan either, this isn't a shaming post at all I promise) Could that actually potentially be genetic? Like perhaps something is wrong in their genes and their bodies are telling them not to reproduce?

Her older brother actually had an accidental son and gave up his rights to him. The son is 6 now I think, and has really severe autism.

There are large age gaps between them all and they were all raised differently so I feel like it wouldn't be because they were around all their siblings all the time or something due to their childhoods.

I've heard of something similar before in both humans and animals where if something is genetically wrong, or there's an undetected disease or deformity, it can actually have an impact on if the animal or person wants to reproduce. This could possibly make sense, especially with the issues her nephew has.

It's not something I'm thinking too hard about, we were just having a conversation about it and it got us both really intrigued. Maybe her and all her siblings carry some kind of deformed gene or something. Maybe it's just coincidence. She's not really concerned about it or anything, just an interesting thought. Anyone have any input?

Literally not a eugenics question lol. I hate kids too. I just think it's really interesting and a good science question.