How do you warn someone about family?

Question

I need some advice.  For back round my “FIL” is a real POS.  12 years ago he plead guilty to essentially kidnapping and being sexually inappropriate with his preteen step daughter.  This was not the first allegation of him preying on little girls, just the first time he got caught.  He’s a predator of opportunity and 3 times has preyed on immediate female family members.  My husbands brother refuses to believe any of this, and thinks his father took a deal to protect his elderly parents from going into financial ruin defending him.  It’s all super convenient he was black out drunk and could remember nothing of the incident.  Recently my BIL and his fiancé announced they were expecting twins a boy and a girl.  There is no way I’m not making sure his fiancé is aware of the danger.  I’m just not sure how to go about it tactfully.  We’re not super close mostly just talk on Facebook.  I don’t want to cause problems I just want to make sure she knows who this man really is, and not to leave her daughter alone with him.
Ok so small misunderstanding: I am totally going to say something I guess my question got lost in the explanation.  I don’t want to cause her any extra stress during her pregnancy, do you think it would be better to say something now or wait until after the babies are born

Answer

Just tell her, it might cause a family fallout but that is a small price to pay if it means the child is protected from this monster. If she chooses to ignore your warning and allows the daughter contact with your FIL then a call to CPS is in order.

Answer

What happened in my family was also "hush hush". I didn't know until I was like 14 that I was actively visiting and spending time with a CONVICTED predator that had multiple victims. The person he hurt last decided to tell my sister and I so we could make that decision on our own. Haven't spoke to him in 10 years and I hate when people talk about him like he isn't scum of the earth. Please tell her, your BIL won't.

Answer

If she's close enough physically, I'd invite her to lunch and let her know it's important and serious and be direct with her. If not, I second asking her for her number and a good time to call where you two can talk privately about something serious. 
She definitely has the right to know. Especially if it was her husband defending the man.

Answer

Dont beat around the bush. Invite her out for a lunch date or just call her.

Answer

I would message her asking for her phone number and a good time to call her so you can speak over the phone instead of back and forth through fb.

Answer

Totally been there. My sister in law is an actually psycho. Before she got married I warned my now brother in law. My father in law (step dad to my sister in law) also pulled her husband aside and warned him about her past. He still went ahead with the wedding and they are now 2 years later going through the divorce process. I personally felt guilty not warning my brother in law. My sister in law has a vicious past...

How do you warn someone about family?

The Top Baby Tracker App: Embrace New Beginnings with Tender Care

The Top Fertility Tracker App: Your Path to Achieving Pregnancy

The Top Pregnancy App: Nurturing Your Journey to Motherhood

The Top Period Tracker for Empowering Your Menstrual Health Journey