How are you related to your sister-in-law's grandchildren?

Answer 1

The children of your uncle are your first cousins. The children of your first cousins are you first cousins once removed. Thus the grandchildren of your uncle are first cousins once removed.

The related link I will make below explains how all this works.

Answer 2

Your sister-in-law is either the wife of your brother or the sister of your spouse.

In either case, her children are your nieces and nephews and her grandchildren are your great nieces and great nephews. You are great aunt or great uncle to her grandchildren.

However, if her grandchildren are descended from children she had before she became your sister-in-law (i.e. from a previous marriage), neither her children nor her grandchildren are related to you.

Answer 3

Yes, unless you, your grandpa or your parent who is the child of your grandpa, were adopted.

Answer 4

Your grandparent's first cousins are your first cousins, twice removed.

The grandchildren of your grandparent's first cousins are your third cousins.

Answer 5

Your grandfather's sister is your great aunt. Her son's daughter is her granddaughter.

The grandchildren of you great aunts and great uncles are your second cousins.