Welcome! I just use organic coconut oil you get at grocery stores, I do 1tbs in the evening on top of their food. I think the best yogurt is plain greek but I'll let someone else chime in, I only used yogurt a few times.
I think apoquel is the strongest you can go so I don't know if adding Benadryl will help or not. I'd see what your vet says about that. I hope you can get the allergies to calm down! My EB doesn't have them but I have a pitbull with environmental allergies, they are hard to control.