I know the sk8 boys will probably never get canon girlfriends because it would upset the fans and ruin the relationship ambiguity, but I have an idea for Adam: his aunts arrange for him to meet a woman, but she turns out to be gay and in love with her lady secretary. The two chat and decide if they're to be married off by their relatives, it might as well be to each other. The secretaries marry too. Now they can all do their own thing in private, produce an heir or two, get on with their lives.
Perhaps if Japan legalizes and normalizes same sex marriage in the future the couples will swap partners.