Suggestions for online safety??

[oklahoma]

My SDs are 12 and 13.  We just restarted every other weekend visits, but it is a graduated schedule, so right now we see them about 9 hours EOW.  Recently, I have been in different situations where the topic of online safety/online sexual predators has been discussed.  (I haven't been looking for information, it just keeps finding me.)  So my concern is growing about SDs.

BM is CP.  BM is not the brightest bulb, and I sincerely doubt her ability to monitor SDs online, especially since OSD has had her own laptop now for about 2 years, and both SDs have their own cell phones now.  I know we could talk with SDs about online safety, but when it comes to actual rules that are practiced, we know SDs know how to work the situation--Tell Dad exactly what he wants to hear.  BM will only communicate with us through an attorney--that adds up!  (Stepdad is also non-communicative, I've never spoken with him in the 7 years I have been with my husband and have only seen him in court.)

Does anyone have suggestions/experience in how to have a real discussion with CP about a real concern?  My husband would LOVE to get all 4 parents together and discuss the issues, go to parenting classes, whatever.  BM keeps pulling the "he's so controlling, I can't talk to him" card.