You don't write / act like you've ever raised any kids, that's all. It would very hard for children to grow up in a situation where the parent makes assertions then provides no proof or reasoning when asked about them. Like you. That's what I know.
As far as your sister - in - law, doesn't your shithole state or county have a Child Protective Services program? Why don't you report her? Your brother's wife? If he's not taking the kid away, just shut the fuck up, it's not your business and no one's interested in your opinion about it. .
Oh, right, an 8 second video on TikTok makes your point. No context, no hearing what the kids had to say about it, or parents reactions. I mean, for all we know from that video, a parent's group asked for it. And there are no confused kids in it, at all.