If children are being abused, continue to contact CPS (at that time or shortly after) and/or police (at the time of the abuse). This is all you can do. I don't think from the description of your relationships with your children that anything you can say to them will have any effect.

Your ability to help (again from the descriptions you have given in other posts about your relationships with the adult children) will be as reporter or voice for the children, who have no ability to protect themselves.