Background: my adult sister is in a relationship with a man currently serving time for domestic violence against women and children…they got together about 6 months ago, shortly before he started his sentence. BF has a history of coercive control. DS sadly has a history of being attracted to these sorts of relationships - she has psychological issues, past trauma but also refuses to engage with therapy. I have tried in the past to chat to her and encourage therapy/behaviour change around relationships but she won’t listen.
Anyway, over Christmas when staying with family, it becomes apparent that the BF is calling DS 4-5 times each day from prison. Phonecalls were often taken in the same room I was in, so I was party to half the discussion . Seem to be discussing DS day and movements in lots of detail - what she has been up to etc (obvious further red flags).
DS several times starts talking about what she has been up to with my 3 DC eg opening presents, going to the park together etc, refers to them by their names and clear she has talked about us all before to him as part of the general conversation. (NB DH or I are always present when she is with DC due to aforementioned issues).
I am left feeling unsettled that information about my family has been shared with DS BF (names, ages, what we are up to etc). I have never met him and never plan to. I don’t think he would have any reason to use this information but who knows how things will work out between them and I feel uncomfortable that he knows who we are, given his horrendous history.
AIBU to speak to my sister and ask her not to discuss me, DH or DC again with this man?