some of the blackberries have some yellow spots on part of the berry
It sounds like White Drupelet Syndrome.
These links have more information.
https://www.gardeningknowhow.com/edible/fruits/raspberry/white-drupelet-syndrome.htm
https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-calico-virus.htm
My blackberry bushes (thornless) have sent out new shoots that are about 12 ft. I need to trim them Can I do that now I know the ones that bare fruit this year will not produce next year so when do I cut those also.
You can do summer pruning when the plants are done fruiting.
This link will help you.
https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
We have been seeing these reddish brown spots on the leaves of some of our blackberry plants. The edges of the leaves get brown and dry as well. What is this and how do we correct it? We have been using a 3 in 1 organic fungicide/insecticide spray every week for the past few weeks. Temperatures have been very hot and humid for the last month. Blackberries are watered with drip irrigation but perhaps not enough.
This sounds like Blackberry Calico Virus.
This link will give you more information.
https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-calico-virus.htm
This year after removing old canes, new canes have gone crazy, 15 to 20 feet long. Can you trim them down before winter?
These links will help you.
https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-bushes-in-winter.htm
https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
I have been growing the blackberries for about 20 years. Several years ago I noticed their growth pattern changing. Branches becoming longer, some of the fruit with dry seeds. This year they grew extremely vigorous, and most of the fruit either did not set, turned brown, or so many seeds that were brown they were not good to eat. I found on your site that they had a disease and needed to be completely torn out. Is this so , and can I replant in the same place?
This does seem like a fungal disease. You must first get rid of the disease before you can replant in that area, or they will just keep passing the disease on. Here is an article that will help: http://oksusag.okstate.edu/uploaded_files/SmithBlackberriesDisease.pdf
There are no berries this year. Plants are 8 years old and have supplied abundance supply of berries. About 10 feet apart I have planted raspberries. The raspberries plants are 3 years old and no berries. Would these raspberry plants effect the blackberry plants?
I don't believe that this is the cause. Has it been overly dry in your area? I am including some articles so that you may find exactly what is happening: https://www.gardeningknowhow.com/edible/fruits/raspberry/
Healthy looking plants, but they have no blossoms or fruit. They are 4 yr. old well established plants.
Unfortunately, there are so many things that could cause this. I am posting the link to an article that will explain the most common reasons why this happens. This will give you more information: https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberries-not-fruiting.htm