My brother married his high school sweetheart who has five siblings who all have kids that have grown up calling me aunt. What relation would my sister in law's nieces and nephews be to me?

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    In English law, your sister-in-law's nieces and nephews are no relation to you. (I'm in the same situation: my brother married his university girlfriend who has a number of sisters with children. I'm not related to the children.) However, if they call you Aunt, then nephew-in-law might be a suitable epithet.
    – Andrew Leach
    Jan 3, 2016 at 21:00
  • There is a term aunt-by-law though this is usually the wife of one's parent's brother. You are proposing something that is one step further removed so I am not sure whether it can apply. In any event it seems you are an aunt-by-courtesy.
    – WS2
    Jan 3, 2016 at 22:27
  • Clearly you’re their aunt for all practical purposes. But since you don’t share any common ancestors you are of no relation at all.
    – Jim
    Jan 3, 2016 at 22:41
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1 Answer 1


Considering that the proper term for your spouse's brother or sister would be your co-brother-in-law or co-sister-in-law and though this term would be highly uncommon, it could be suggested that their kids would be your co-niece-in-laws and co-nephew-in-laws. However, the term co-sibling-in-law is believed to have stemmed from translations of South Indian languages, which could be the reason for its wordiness.

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    Why prepend the "co" in your examples? I'm unfamiliar with that construction.
    – The Nate
    Jan 8, 2016 at 12:12

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