I suppose you could call them an Aunt-in-law, but I always addressed my spouse's Aunts as "Aunt".
If you mean is it legal for you to possess a handgun given to you by your father-in-law, the answer is, probably. In most states, it would be legal, assuming you and your father-in-law live in the same state. Person to person transfers are legal, but a few states require registration or paperwork to legally process the transfer.
Your sister's sister is your sister.
Yes, the sister of your spouse (wife or husband) is your sister-in-law. In addition, the wife of your brother is also your sister-in-law.
Sister My Sister was created in 1995.
If your sister in law is your wife's sister then she would be nothing to your sister. However if your sister in law is your brother's wife then she would also be your sister's sister in law.
There are two ways you can have a sister-in-law. In one case, her sister is also your sister-in-law and in the other she is not. Your sister-in-law can be the sister of your spouse. Then your sister-in-law's sister is either your wife or is also your sister-in-law. Your sister-in-law can also be the wife of your brother. In that case, your sister-in-law's sister is not related to you.
Real sister, half sister, or step sister
The duration of Sister My Sister is 1.48 hours.
Sister
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Your sister and your wife's sister are not related to each other.
The English language has no special term for the sister of your sister-in-law if she is the wife of your brother. Her sister is not considered to be related to you.If your sister-in-law is the sister of your spouse, her sister is also your sister-in-law, unless she is your wife.