Or maybe it's like "last Love Live doujin with this crew" since the next set of idols is a whole new set of girls.
And Arisa, you'll have three sisters if you tie up the knot with Yukiho. But then...if Honoka ties it up with Tsubasa (or Kotori or Umi; your ship doesn't matter in this case) would she have four sisters? I dunno. Would you consider the wife of your in-law also your sister? Maybe it depends on the case depending on how close your in-laws are to your significant other.