Our tomato plants (Fantastic variety) are not doing well. They are very small when ripe and have very tough skins. What are we doing wrong?

The Fantastic variety of tomato is not a very large size tomato typically, but should be medium size. It is difficult to say for sure, but the tough skins tells us that they are probably lacking water Perhaps the soil is not of the consistency to hold the moisture you give it. You could fertilize with vegetable food (8-20-20). Good luck.