Nephews and/or Nieces
Your brother's wife's kids would be your nieces or nephews.
Your borther-in-law's children are your nieces and nephews. You are their uncle or aunt, as is your spouse.
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.
Your brother's child's children are your grandnieces or grandnephews.
If your brother (or your sister) has children they are your nephews (males) and nieces (females).
Your brother's children would be your nieces and nephews.
Your brother-in-law's children are your nephews and nieces.
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.
No. He had a brother patrick who married but had no children.
Nieces and nephews are the children of your siblings.
The children born to your siblings are your nieces and nephews.