I think it depends on the dogs. It can work out. But it can also cause problems. I think this does not have anything to do with lines or genetics. I think it is something you certainly could not determine by eight weeks in the litter. So it is a huge gamble every single time.
I have raised several littermates, and left them together for up to fifteen months. None of them are more concerned with each other than me. But a pup that went to its home at 4 months and came back to me at six months, and then kept totally separated from the other dogs, due to a serious injury -- that dog is far more interested in dogs than people, at home or abroad. But it is true that it is more than double the work. Socialize the singly, potty training is a blast when you have two or even three that need to go out first thing in the morning, and than need constant supervision. Training is separate too. And passing out treats to three alligators at the same time -- I marvel that I still have my full complement of fingers.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC