If his mouth is "horrid", why isn't he getting dental care...?!
I don't know if you've ever personally had any dental pain, but if you haven't - it's *extremely* painful. PLEASE get this poor baby the dental care that is clearly needed
. It should not be neglected - it's not fair to him and it's cruel if he is in pain, which is likely if the smell is horrid.
As far as body smells, the vet should assess / test for a yeast infection and seborrhea, as well as other skin conditions. Are there any areas of red patches or anything...?