When referring to in-laws using 義理, do you use the familial term relative to yourself or to your spouse?

Question

When using terms such as 義理のお兄さん and 義理の弟, do you choose お兄さん vs 弟 relative to your own age, or relative to your spouses age?

If you are older than your spouse, but said spouse's older brother is younger than you, which term is appropriate?

I assume the same applies to the word-versions such as 義弟?

Answer 1

Relative to your spouse's age.

In your case, you'd have a 義理の兄(義兄) who is younger than you. And you'd be his 義理の弟/妹 who is older than himself.