"I remember reading that in Japan sometimes homosexual men would adopt their lover into their family, so that they would be on the family register and share the same name/clan allegiance. I forget where I first saw that and I must not be googling it right because I can't find the explanation again, though. sob sob sob. Anyway."

I dunno about real life, but there's a BRILLIANT Xxxholic fic by Ookami Kasumi "Kitsune Bi" that uses this concept. [ez waiting patiently-but-not-really-patiently for update]

http://www.fanfiction.net/s/3843949/1/Kitsune_Bi_An_xXxHolic_FanFiction