It was fascinating and very informative to have a dual-sired litter work out. There are many reasons to attempt a dual sire litter, but what frequently happens is all the pups are from a single dog, or if you're really unfortunate there are no pups from either dog. Chalk was very different to the other pups, both in his personality and physical build. It's one thing to have a litter and speculate that a particular trait comes from a sire because you saw it in another litter you had, or an earlier litter the bitch had by someone else didn't show it, but it's another thing entirely to have a pup from a different sire exactly the same age to compare with!
Best wishes to all the pups and their new families.