Thank you for the additional information.
The first thing I want to say is that here in Florida with a dog that has allergies Flea prevention every 3-4 weeks is a must. They never go away down here and most dogs with allergies will also test positive for flea allergies. When a flea allergy is present it only take the bite of one Flea to set off a reaction. This is because they react not only to the bite but the saliva and the flea dirt left behind. I would be sure to use this on both dogs every
Next I would suggest allergy testing so you know exactly what the allergies are. VARL is the blood test we use and it works great . Once tested you have the option of having serum made to desensitizing him.Link
Another thing that we have been having great success with is giving 1/2 teaspoon of raw honey daily. Now you want to find a honey that is made locally so it is specific to your area and get it in raw form. I would look for a local bee keeper in your area. The reason we are using the honey is because the bees go around collecting pollen from all local plants so by giving the local honey you are introducing these allergens in a good way so the body builds and immunity to it.
As for drug therapy Atopica is the best solution we have found. Normally we give this daily for 5-7 days then taper off to 1-2 times per week . This not only works better but is safer then long term steroids.Link
For itching Oral Benadryl at a dose of 1-2 mgs per pound of body weight every 8-10 hours.
Resicort which is a leave on conditioner is also great for allergy dogs. LINK
I hope this helps give you additional options to help PowerStroke. Please reply back if you have additional questions or concerns and I will be happy to continue.