Yes, it's possible. Because the niece's father and the husband share the same father so any offspring of the husband would be related. There is no specific name for this relationship, but presuming no illegitimacy or adoption, there is a genetic connection.
yes
great nephew
The possessive form for the plural noun great aunts is great aunts'.Example: My three great aunts' house is a great place to visit.
There are Aunts, great aunts, great-great aunts, et al. A second aunt would be if you have two aunts and you prefer one over the other. But no there isn't.
The cousins of your in-laws are not related to you and neither are their parents. However, the parents of your spouse's first cousins are your spouse's aunts and uncles, and thus your children's great aunts and great uncles.
If your great uncle married into your family some of his nieces and nephews are your aunts or uncles (or your parent) and some are not related to you at all.
Your great aunt is the sister of one of your grandparents. The wife of one of your grand parent's brothers is your great aunt by marriage. Another way to look at it is that your great aunts are the aunts of one of your parents.
Your great grandparents' brothers and sisters are your great great aunts and uncles.
First cousins, twice removed. Aunts daughter is your cousin. Aunts daughters daughter is cousin once removed Aunts daughters daughters daughter is cousin twice removed.
Great aunt.
No, great-aunts' is the possessive form of the pluralnoun, indicating that something belongs to two or more great-aunts.Example: Both of my great-aunts' birthdays are the same day.The possessive of the singular noun great-aunt is great-aunt's.Example: My great-aunt's birthday is on Friday.
The Iroquois lived in longhouses. These longhouses were anywhere from 70 feet to 300 feet long. (about the length of a football field) 5 - 20 families would live in a longhouse, with all of their maternal relatives. (your mother, sisters, aunts, great aunts, grandmothers...) and their husbands. All these women would be of the same clan.