
NO!
Even though these are tiny little dogs they are ALL dog as im sure you know. Two males growing up together, egging each other on in puppy hood to wreck things etc, then the possible conflict that comes when they begin to mature, hmmmmmmmmm, nope, i wouldnt let someone do it if i had that choice, nor would i want to own two terrier litter mates.
If the buyer REALLY wants two puppies together, and knows how much more hard work two is than one, then advise him to get a dog and a b itch, rather than two the same. I have to say thought, its still a bad idea, with much greater chances that one of the two will end up being returned.
Em