You are cousins by marriage.
Depending on local and state law, it is a marriage to a blood relative that is a cousin or closer. Some states allow marriage between first cousins, but the Federal Govt still frowns upon it...
I'm not completely sure but I would say that it is English Law. Because from my research I found under "common-marriage law", the first Act of Marriage occurred in the 1700's. At the time, there was not a USA but there were 13 colonies, and Britain ruled over them. Britain and England are both the same country, so I think it's English Law.
The two would be first cousins. First cousin marriage is legal in many jurisdictions. You need to check the law in your particular jurisdiction. You could inquire at the office where marriage licenses are issued.
No, first cousins can not marry in Texas.
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.
My sister in law is calling her husband's family cousins to my daughter. Is this correct?
Your cousin' spouse becomes your cousin by marriage (cousin-in-law). The reason for this is that they have the same relationship to you.
No. Most states prevent marriage or sexual activity between you and your first cousin, aunt / uncle, parent, step-parent, grandparents, great aunts and uncles. Cousins more distant than first cousins are perfectly acceptable in the law in the United States and nearly everywhere in the world. First cousin marriage is acceptable in a number of states, Colorado for example. Most people have no idea who their fifth cousins are unless they have done some serious genealogy.
In New Jersey, as in most states, it is legal to marry some relatives, but not others. New Jersey marriage law (Title 37 New Jersey Permanent Statutes) forbids marriage with your children, parents, grandparents, grandshildren, siblings, aunts, uncles, nieces and nephews. Some states also forbid marriage with a first cousin, but New Jersey does not. First cousins, once removed, and more distant relatives, such as second cousins, can marry.
The English language has not special name for the cousins of your spouse. You could just call them by their first names like you would your friends. If you really like them, you could decide to call them your cousins.
Your daughter and your sister's son are first cousins to each other.