Remy: Thompson seedless are naturally small berries. What you are seeing is somewhere near the normal berry size of that cultivar. Commercial growers achieve larger berries by spraying gibberellic acid to first thin the fruit off each cluster and then to plump up the remaining berries. They also use other tricks like girdling the trunk. You could do this. It's not that hard. But it doesn't increase the flavor or sweetness and may do the opposite. Doing a better job of pruning, thinning, and other cultural tasks can increase berry size somewhat if they are limiting factors. Commercially berry size increase is used only for Thompsons destined for table grape use or other special applications like Jumbo raisins. The normal raisins are grown with small berries just like yours. So the vast majority of Thompsons are grown like yours with small berries.

You'll get a higher yield if you do. Don't boil, just simmer. Carol

I grow a few varieties of grapes but not sure I would call myself an expert. From your pictures, it looks like you have one or more fungal infections on your grapes. The treatment is essentially the same if it is black rot, downy mildew, phomopsis cane, etc. At the end of the season, you'll need to prune off the infected canes, clean up around the vines, and make sure that there are no infected grapes laying around. Start the vine on a spray program next year and it should clear up. My vines looked worse last year but this year I followed the spray program and they are nearly perfect. The season isn't over but I may have more grapes than I know what to do with. Although our regions are a bit different, here is the guide I used to manage the spray routine. Midwest IPM Guide

There is different grapes, tickled pink is an european grape I think, there is muscadine, American, and european