Yes, those are hens for sure. The squat means she is ready to accept a mate and lay. Your girls are just latebloomers! Sometimes, folks will think they are buying one breed, in your case red sexlinks, then they realize that they not only got a different, though similar-looking breed, but a...
Here's a dumb question for you.... are you sure they're hens? Though that is not late for most chicken breeds, it is late for sexlinks, who very often lay before 18 weeks old.