The Mystery Of Six Portaits

The antique dealer said they are from the 50s and that she bought them from an estate of an art teacher in Beverly Hills.  Judging from the style of the brush strokes and technique, I think these are from different student painters.  In fact, two of them have a white unpainted portion of the canvas, suggested some unfinished student work.  Only one was signed on the back "Sheffield '57".  It does make me wonder whether it's the students or the teacher who's really good because these are very well done oil portraits.  The other thing I wonder is why the students did not sign their works.  Are they unfinished and the teacher just took them?  Student artwork not belonging to the originator is unheard of these days but who knows what the practice was back in the 50s.  Are these from live models or photographs?  Are these subjects still alive? All these questions just keep on adding on to the mystery of these portraits.