Hm...I've been toying with that idea for a while now and the one thing that sticks out to me was that Reborn did it on purpose. :/ I'm not sure what country they would have come from but since Reborn has eyes everywhere...it is kinda possible with him. He's always on the look out for people who would benefit the family in some way. Even if they could never become guardians (they'd be more like back-ups just in case) they would still have some use for the family. 

Maybe they had been applying to an international school and Reborn had been keeping tabs on them for a while. It sounds a bit crazy and creepy but Reborn seems to scout for people specifically to join the family.