When it comes to describing the relationship with your spouse's siblings' spouses, "co-in-law" might not cut it. Fortunately, there are other synonyms you can use to describe this familial connection. One option is to use the phrase "in-law cousin," which references the cousin-like relationship between you and your spouse's siblings' spouses. Alternatively, you could refer to them as "in-law siblings" or "brother/sister-in-law" to emphasize the familial tie. Whatever phrase you choose, it's important to recognize the unique role that these extended family members play in your life and to treat them with kindness and respect.