Well, I work with kids and when there is a Lice outbreak we wash everything in the school. I wouldn't have thought that a dog could get lice,but since we're told Yorkies and Maltese have HAIR...then it does make sense.
If your Vet is saying mellow out then your probably ok. Does he know they have HAIR though?
Tea tree oil works to repel lice. Also, lice like CLEAN hair so forgo the the once a week bath.
Maybe use some oil and detangler to get product on the fur and repel the lice.
Dirty hair and tea tree oil works for kids too...of course after you've treated it for lice and washed everything in sight