I'm not certain what your exact question is, but you are totally right to be concerned as a parent as well as to be upset by this disturbing news. I have similar issues in my family, and I simply refuse to have contact with or allow any other family member to put my children in contact with the person that did these things. Also, most communities have counseling available at low to no cost if that is a concern. You may want to consider at least a few meetings with someone to talk about this news and work through your feelings and your response.
Nephews and/or Nieces
your nephews
Children of your siblings are nieces and nephews. Children of your spouse's siblings are still called nieces and nephews, but you are not related to them by blood.
Nephews are the sons of your brother or sister. Therefore nephews who are not brothers to each other are first cousins to each other.
If your brother (or your sister) has children they are your nephews (males) and nieces (females).
Your brother-in-law's children are your nephews and nieces.
Your brother's children would be your nieces and nephews.
Your brother's wife's kids would be your nieces or nephews.
Your brother's child's children are your grandnieces or grandnephews.
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
No. He had a brother patrick who married but had no children.
Your sister-in-law is either the wife of your brother or the sister of your spouse. The children of your brother's wife are your nieces and nephews, since they are also the children of your brother. In some cases they may be your sister-in-law's children from a previous marriage. Then they are not related to you at all. However, if they are very young, it may be convenient to call them your nieces and nephews anyway. The children of your spouse's sister are always your nieces and nephews.