Welcome to the forum, greendream. Something's going on but I'm not sure what. If you were to replace them with more plants do you think you wouldn't have the same issue?
Shriveling tomato leaves can be several things. You might want to look at this article:
Curled leaves and flowers on tomatoes
What type tomato plants are these? With the lower leaves already yellowing it doesn't sound good.
You might want to add your location in your profile so folks will know where you're located...it can make a difference in the advice that you receive. I'm in hot and humid south Alabama and have a TON of disease issues with tomatoes.
While other's here have relatively few problems growing them.
