> If it was mange, I'm guessing that at least one other member of the gang would get it.
If it were sarcoptic, then yes, the others would get it and you too most probably - it's very contagious.
Demodectic mange ( Demodex) is an already present organism which is dormant in many affected animals, auto-immune in it's nature and often only shows it's self in puppies, youngsters, pregnant bitches and others under stress.
A skin scrape is needed to identify in puppies but it is notoriously difficult in adults because it's often deep in the follicles of the skin.
A visit to the vet will ease your mind.