Your son and your nephew are first cousins to each other.
Their daughters are second cousins to each other.
If I were you, I would break up with him. Not only because he doesn't like your daughter, but if you think about it; How would that effect your daughters life, and her relationship with you.
They would be great nieces or great nephews.
It Depends. Not every daughter father relationship is the same. There are daughters who hate their father. And their are some who love them because there he onlyones there for them. Everybody's different.
Technically there is no relationship. When introducing her, you would refer to her as My daughter's mother-in-law.
Your nephews' children would be your children's cousins. They share a common grandparent, as their parents (your nephews) are siblings to your children’s parents. This familial relationship creates a bond among them, typically fostering a close connection within the extended family.
The correct term would be "daughter's" if you are referring to something that belongs to one daughter. For example, "My daughter's book." On the other hand, if you are referring to something that belongs to multiple daughters, you would use "daughters." For example, "My daughters' toys." The use of the apostrophe indicates possession or ownership.
Your brother's children would be your nieces and nephews.
She would be your Great/ Grand Niece. Seeing as you are her Great Aunt or Uncle.
A cousin, in all those difficult cases they are your cousins
There would be no relationship as you do not share a common ancestor. If your brother-in-law is married to your sister, then her daughter is your niece, her husband would be referred to as your niece's husband.
Every father daughter relationship is different. Probably most fathers would want their daughters to know that they deserve to be treated well, and that they should treat others well. They would want them to know their self worth.
I think it would be your daughters 2nd cousin. (: