How old are your Nieces? If they are younger they are not going to be able to lift an older vintage machine unless it is a Featherweight or a Singer Slant series aluminum machine. Most of those old cabinet queens and portables are cast iron. I love my old machines but I started out on a Brother cs6000. I would get them both a new, electronic machine. Either a Brother, Kenmore or Janome so they can learn to sew on machines like they see on that runway show on TV.
When they come to visit, you can let them sew on a vintage machine and show them the differences in stitch quality, versatility with attachments and how quiet they are.