So a spouse I am considering for gen 2's sister lives in a house with gen 2's unique best friend. No one else even knows the guy. But what if Sister becomes best friends with Unique BF when she moves in there after the wedding? She's not a household member anymore right, so it doesn't count? Come to think of it, I don't think I would even know what relationship they would have. Unique BF is pretty old anyway so he'll likely die soon.