It certainly could be a yeast infection. The key thing to understand about yeast is that they are always in competition with bacteria. And, steroids take down the body's ability to keep yeast from overgrowing, but will help the dogs be more comfortable.
Some vets will use an systemic antifungal on dogs, which are like antibiotics. I have done so, but often find that simple bathing works more effectively.
You would want to use an antibacterial/antifungal shampoo. You may be able to find one at the local pet store, on amazon, or even over the counter at your vet. Make certain it is antibacterial and antifungal. Otherwise you will not solve the problem
Also, most yeast comes from the ears, so you should be cleaning the ears well until this problem goes away. Often dogs spread it to each other. It is not easily spread, but dogs love to lick yeasty ears, then lick their own fur or the other dogs. This will spread it. Now you have more than one dog with a problem.
This can turn in to a lot of work for awhile, but it also will save you potentially a fortune. Clean their ears at least every other day until the problem is resolved. Bathe them twice weekly, with the appropriate shampoo, until the problem is resolved. Make certain to rinse well, so you don't overdry their skin, which can set them up for problems.
The last thing to consider, since yeast, and bacteria, are opportunistic, is whether something else is going on--allergies, food allergies
, some sort of disease, etc. This will allow the yeast and bacteria to overgrow, but is truly your main problem. You can control the yeast symptoms, but they may come back if there is something else going on.
Let me know if you have additional questions.