1 Teaspoon per gallon, and you can foliar feed both the epsom salts and the B1. I would mix up about a teaspoon/gallon and feed the plants but also take a bit of the solution and foliar feed them for quicker results. The damaged leaves MAY not recoup, but to the new growth you will be their hero, lol
Good luck, but trust me they are not even close to being too far gone, you can doctor them back to health in probably under a week.
By the way Granddaddy is great, it should start purpling around the 3-4 week of flower