They did do a skin scrape for mites, correct? if that cam back negative, then ALL of these issues are probably related to the food
the areas that are moist and red... they are hotspots, which you need to shave the are of the fur, clean with peroxide and then keep the are clean and dry with witch hazel (if you can get that).
the areas that are white with no fur.... I'm thinking looks like mange, which is usually due to mites. skin scrape will be needed to confirm
the other smaller areas that look dry --- might be a staph infection which will need a strong dose over many weeks of antibiotics.
the food you have pictured, if you look at the ingredient list, it is all grains, there is no meat in this food at all. it is grains, fat and liver.
COMPOSITION: rice, wheat gluten, wheat, animal fats, maize, maize gluten, husked oats, hydrolysed poultry liver, minerals, soya oil, beet pulp, fish oil (source of EPA and DHA), flax seeds (source of omega 3), fructo-oligosaccharides, borage oil (source of gamma-linolenic acid), marigold extract (source of lutein).
What other foods do you have available to you?