Though 16 day old puppies is ALOT different than 10-12 week puppies, the first thought that came to my mind as I read your post was this:
Reading your post took me back to when we first brought each of our fur babies home. For the first week(s) I remember we wondered...."He/She is so quiet, Will they ever bark?" Well duh, of course they will.........and boy do they! LOL Now it's more like..."Will they ever be quiet?"
I would assume the same holds true for Scarlet and Ruby. They'll will be letting you know their presence before too long. For now, they must both just be happy, content babies!