Yes, he is their great uncle.
uncle.
Relationship sequence:Your uncle is your mother's brotherHis children are your first cousinsHis grandchildren are your first cousins once removed
Your niece in-law, or your niece by marriage.
Phillipp uncle
Your grandmother's brother is your great uncle. Your great uncle's grandchildren are your second cousins.
Your husband is great uncle to your niece's son (your great nephew).
Your great uncle! (no blood relation there, but still your uncle:)
You are an aunt/uncle-in-law! Congratulations!! You really are; because you're an aunt/uncle to your niece you are now an aunt/niece by marriage to her husband.
Your sister's husband is your children's uncle. They are his nieces and nephews.
The English language has no specific term for a relationship between your uncle and your wife. Your uncle will usually call her "my nephew's wife" and she can call him "my husband's uncle."
Your mother's brother is your uncle. Your uncle's brother-in-law is either the husband of his sister or the brother of his wife. The brother of your uncle's wife is not related to you. The husband of your uncle's sister is either your father, or the husband of another one of your mother's sisters and thus your uncle.
You aren't. Your mother's brother is your Uncle. Your Uncle's aunt is one of your grandparent's sisters - your grand Aunt. Her "only" niece could be your Uncle's sister or cousin, you don't provide enough information to know. If it's your Uncle's sister she is your Aunt. If it's your Uncle's cousin she is your first cousin, once removed. If it's your Aunt, her mother-in-law is simply the mother of the man she married. Your uncle-in-law's mom. The "in-law" thing does not carry past the Uncle-in-law, or you'd be "in-law" to the world. So no relation to his mom, or the mom's husband. If your cousin (once removed), her mother-in-law is simply the mother of the man she married. Your first cousin/once removed-in-law (not a generally recognized relation). Were it to be, it still doesn't go past the cousin/once removed-in-law, or you'd be "in-law" to the world. So no relation. Therefore no relation to his mom, or the mom's husband. (The phrasing "mother-in-law's husband" connotes that the man is a second husband and no relation to the Uncle-in-law or cousin/once removed-in-law - else such would have been described as "father-in-law" not "mother-in-law's husband. Therefore, even moreso NOT a relation.)