But they banged on about Charles' dysfunctional upbringing
Charles banged on about it himself so they aren't doing anything he hasn't done.
That’s a difference worth at least considering, though, isn’t it? Telling your own story in public versus telling someone else’s. This is highly personal stuff and clearly there has been some upset in the family, in more than one generation, so feelings are tender.
We have some eccentric branches to my family, some “interesting” choices, some repeated patterns, and as a result some of my relations had unconventional childhoods.
My gut feeling is that - if for some reason I/we were media worthy and the interviewer knew enough to ask about these eccentricities - I would feel entitled to speak about my own (distant, diluted) experience of it but not, for example, about my parent’s, grandparent’s or sibling’s thoughts on or experience of it.
If I were to write about the whole saga, for publication, I’d only do it after the older generation were dead.
Different if you’re chatting privately to your friend or your spouse about patterns you can see repeated through the generations, of course. Similarly, if you’re writing a private family history for family members only.
If I were likely to actually give such an interview, I think about where the line is even more carefully than I am now.
I think it is hard, really, for most people to imagine being famous and the ramifications of that.