Q.If my peach tree is diseased, will the seeds be diseased too?
My peach trees have been diseased for a couple of years and we have had no success in treating. We are cutting them all down; however, they are heirloom so I am wondering if the seeds would be diseased or could we use them to regrow?

From my research the seeds very well could also be diseased, depending on the issue with the parent plant.
I would advise purchasing new seed if propagating your own tree is the goal.
https://www.gardeningknowhow.com/edible/fruits/peach/planting-peach-seeds.htm
https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-care.htm