Ouch! That sounds like a bit of a mess with no clear answers...

If the one vet who checked the dog on the other yard said it was yeast, you might do some reading on line about yeast infections and treatments, also look up fungus.

I wish I had more info for you but this is all I can think of to try as there is a lot out there on the net.

I do remember cleaning ears on one of my old dogs with an Apple Cider vinegar and water mix, and I think ACV does help get rid of yeast. Might be worth reading about that too.

Also look up Tea Tree Oil as I think that is good for things like this, but it has been a long time since I read about all this stuff. Tea Tree Oil has a lot of uses but it is strong stuff too.

I hope others will post and have more help. Good luck with this and I hope you get to the bottom of it as ears are pretty sensitive and it is now causing other problems.