Patty, here are a few suggestions:
1) Definitely have another photo session! I don't mean this personally, but It puzzles me why artists would rather work from bad references than GO BACK AGAIN!
If I can, I try to schedule more than one session, just because people are usualy much more relaxed with me the second or even third day. Of course that is not always feasible, but if these people live in your area there is nothing stopping you. It is not a sign of being unprofessional; rather, it is an indication that you are taking the time to get it right.
2) I agree with the advice to avoid toothy grins. Tell them not to smile. But get them talking and talk to them. As they listen you might get some interesting expressions.
3) Try other poses in different lighting conditions. Sometimes you can start with one or two ideas and end up preferring another, completely different idea. What about inside, next to a window or open (glass) doorway? What about under a porch, with one side of them lit by daylight?