Q.Spreading of Blackberry Plants
Will my blackberry plants spread on their own? Is there a way to restart new plants from the plants that I already have?

Certified GKH Gardening Expert
These plants will come back on their own each year provided they have been given proper care. Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/fruits/blackberries/growing-blackberry-bushes.htm
If you are having trouble with your plants, this article will help with their propagation: https://www.gardeningknowhow.com/edible/fruits/blackberries/propagating-blackberries-cuttings.htm