I would think you would call her by her name, same as if she were your son's American mother-in-law.
You can call her by her first name or if your comfortable some son-in-laws call them mom.
Two mother-in-laws call each other "daughter-in-law."
I would think you would call her by her name, same as if she were your son's American mother-in-law.
Your mother's brother's son is your cousin.
Cousin
Your mother's first cousin's son is your second cousin. Your mother's second cousin's son is your third cousin. And so forth.
Your 2nd cousin. He would be your mother's nephew.
Because her daughter will already be like a miniature mother, with skills like that. But a mother likes to fuss over her son, cook tea, do his ironing etc but a daughter in law takes these roles from her.
cousin
Great Aunt.
Either your father, or your uncle.
If the mother's will was probated and the son died AFTER his mother then the property is in the son's estate. His estate would need to be probated. The property would pass to his heirs under the terms of his will or according to the state laws of intestacy. Generally, a surviving spouse is entitled to a portion, if not all, of her husband's estate. You can check your state laws at the related question link below. If the son died before his mother, the property would pass according to his mother's will or the state laws of intestacy as his mother's intestate property.