I think you have several things going on.
The first thing that I saw in your post was the comment about the leaves being purple. Next, the mis-shapen leaves in the pictures. The sunken areas, too. The scorched edges. All of these are signs of nutrient deficiencies. Not saying that there may not be other causes, but I would start with fertilizer problems.
Are these in natural garden soil? Raised planters? Pots?
Have you added anything to the soil?
Have you grown other things in this soil prior to these crops?
Fertilizer problems:
1) Using nothing. Especially if the soil has been growing other crops.
2) Using an incomplete fertilizer, especially if there were plants in there before. An overdose of certain minerals can lead to a deficiency in others.
3) Using an unbalanced product. Something that is not the right fit, does not supply the fertilizers that are lacking in your soil.
If you can get the soil tested, that would be great. There are home-soil test kits, and that is a reasonable place to start.
If you cannot test the soil, then I would study up on the fertilizer needs of the plants you are growing, and try to figure out what nutrients your soil may be lacking.
If even that seems like a lot of work, then fertilize with a complete fertilizer that is labeled for vegetables. Make sure it has some trace minerals (usually iron) as well as N, P and K.
Here is a link to fertilizer deficiencies. The pictures are not much, but there are descriptions that are brief and to the point. The test crop is potatoes, which are related to tomatoes and peppers.
http://customers.hbci.com/~wenonah/min-def/list.htm
