Welcome to pets.ca
. I agree with the advice from the others and would not worry to much about seperating them at this age. Once they hit three months then I would work on seperating them a lot more and work each dog independantly. Seven weeks is very young for puppies and definately to young to worry about good leash walking techniques. Focus more on playing and bonding with them, toilet training etc. Big dogs "usually" potty train easily but don't expect much for another month or so and true reliability will be much longer.
I like this blog http://the-sunshinegirl.blogspot.com/
. The owner raised to labrador litter mates and offers some good advice.
I would also definately recommend this website http://www.dogstardaily.com/
especially the puppy advice from Dr. Ian Dunbar who is regarded as one of the "pioneers" of positive puppy training techniques.
Good luck and we'd love to see pics when you get a spare moment