Very itchy foster pups - help!!

Hello all! I am fostering 2 German Sheppard pups (4 months old) and a 10 week old puppy. They came to me from a high kill shelter state. But all 3 have extremely itching skin. They have patches of missing hair. The 2 GS has crusts on their skin too.

I bathed them with a gentle oatmeal shampoo the first day they came home with me - probably their first bathes ever. Then I did a soothing oatmeal soak the next day (oatmeal powder, green tee, milk, and water). It’s not working and these boys scratches so much. I don’t know wha to do.

They all had a dewormer pill on day 2. Then I gave them simparica trio pill from my own pup’s stash on day 3. They are also having supplement to support a strong immune system.

Is there anything else I can do to help them be more comfy and less itchy? 😢