Kellz has said in an interview before that his own sister molested him when he was a child. I remember that came out when he was first in trial almost a decade ago.
After doing a lil Googles, here's an article this past January 2019 where his own brother confirms these facts that their sister molested not just Kellz but himself too.
R. Kelly's Brother Says They Were Sexually Molested By Their Sister | The Source
Note the reason why his brother knows that Kellz is a sexual deviant is that he too was partaking in the same acts himself because he's in some of the tapes too which is what Kellz was saying not that he isn't in some of the tapes that his brother is in them with him too. Which is another story in itself.
If you listen to his music you'd understand that he talks a lot about forgiving his sister or women. Well, this is where it stems from. Their sister set them on this destructive path.