Two new characters and no their names are Mei (girl) and Kyouhei(boy). International names haven't been released yet. We only know their Japanese names. They aren't related to Hilda or Hilbert (B/W's Main Characters). Just two new younger characters for us to play.
You could have asked in Quick Questions or VM'd me or Jellicent if you wanted a straight answer with no spoilers. Closing this thread since it was a basic question.