Bumps on skin

Here is the poblem I have 4 dogs all of which are scratching. About 3 weeks ago I took one of my females to do a breeding while i was their i noticed one of the other males had what looked to me like and allergic reaction bumps on skin kind of all over i spoke to the owner of the stud he told me that dog was the only one with the bumps and was being treated he was told by is vet that they were some kind of pimples. I left my dog there for a week she was to use another stud not showing these symptoms so to me all was well. It is now 3 weeks later on this past friday i noticed similar bumps on my now pregnant female maybe its stress not as many as were on the male at the stud owners. my wife tells me this weekend she put advantix on the other dog because they were scratching not on the pregnant female of course. One of my males has bone cancer and this morning he is covered in the bumps te pregnant females bumps seem to have gone down but not gone. I called the stud owner he said his dog was treated with antibiotics and is getting better was told by is vet it was not contagious i am thinking it could be sarcoptic mange so i call my vet he tells me to give the boy with cancer some benadryl for the reaction and call back in a couple days. Am i wrong in thinking mang or is his vet wrong in not tating as if it were mange skin scaping came up negative in his dog

please help