Crossposted from tumblr: Halacha question re: marriage

[captainlordauditor]

 if I’m getting married*, how is “relative” defined for the purposes of finding witnesses? I know blood relatives and their spouses don’t count, but what about the sister of my brother-in-law**? What about her husband?

*I’m not

**as in, my sister’s husband’s sister. English needs better words for this