What does one call his/her mother's sister's husband's parents?

I am asking this question for a friend. My friend's sister's husband's parents have become very involved in her kids' lives. She wants to know if there is a relational term her children may officially refer to them as. Thanks for your help!

Solution 1:

For children, relatives at one's parent's generation or above that are not explicitly parents or grandparents or just close friends of the family at those generation are usually referred to simply as

Aunt or Uncle so-and-so.

But that's what you call them to their face. If you need to describe them to other people, usually there's some kinship term or more likely a combination, just like you described. For the very particular relation given, there is no single term in English for such a complicated relationship and so a combination of terms, like "aunt's in-laws" might be sufficient (but would include brothers- and sisters-in-law).

Solution 2:

Your mother's sister is your aunt.

Your husband's parents are your parents-in-law.

Putting those two together: aunt's parents-in-law or aunt's in-laws