You do not want a 6 week old! Yikes!! 

 This is way too young. I keep my till they are 12 weeks old. They need that extra boost from mom and to be socialized more. They are terriers. Yorkies babies can also get hypoglycemia (low blood sugar) if taken away too young and due to stress. They can actually die from this. Sounds like they have no clue and do not want to have to deal with buying shots, vet check, or do poop patrol cleanup. I would put my foot down and say no, I will not take it at this age. Not unless you want to deal with a lot of problems and possible heartache. 
Have you not seen the parents or their home yet?