No way would I do it.
Firstly, they are far too young to be rehomed. If they did get them from a breeder then the breeder gave them a 3-4 week old puppy and that's downright wrong, not to mention two puppies from the same litter. No way would a reputable breeder do that on either count is there any paperwork at all on the parents or puppies? Vet checks? At minimum you're going to have to pay for a vet visit and first shots and probably deworming.
The fact they're stating from the day they bought the puppies not even two weeks later there is now an emergency trip to Australia? Completely fishy
If the price is firm on those puppies then take that $800 and either go to a shelter or rescue and get a dog from them. You'll spend less than half that price and they'll come with being spayed/neutered, heartworm tests, vaccinations, health check, microchip, and probably local license if not more. If you really want a puppy, it's not uncommon for young puppies to be dropped off and while they might not have one right away you should be able to be put on a list for notification is any do come available.
Or save a little more and spend $1000 - $2000 for a well-bred dog from a reputable breeder.
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010