I've now got 14 week old litter mates, A boy and a girl. They get on great and their personalities compliment one another. Phoebe is definately boss and you could see from 5 weeks of age what sort of personalities were developing, Logan is laid back and phoebe is an adventurous, mischievious imp. When any of the other pups return to our house it's Phoebe that pins them down and puts them in their place, Logan will play with them all. (so far as I am aware that the dynamics will change with adolescent behaviour).
Both dogs are walked together with Penny off their leads in the woods and socialise well with other dogs and have pretty good recall, (Phoebe needs more of an eye keeping on her because she runs alittle further and is more likely to ignore you, but I insist that they return on recall every so often just to reinforce my authority)
They also have separate individual walks and training as I fully expect to have 2 well trained pups at some time in the future so practice makes perfect!
They love playing with each other at home and I am conscious that they may bond together, but so far they are still very much at the stage were humans are important to them. I feed them at the same time and they are good together, although Logan is a bit more possessive with his bones than Phoebe, but he knows if he finishes first he dare not take hers. They also sleep together.
Toilet training is getting there, but I have limited them to only 2 rooms, which I haven't done in the past just to make it easier to minimise accidents.
I know I have a long way to go and may encounter problems in the future, but so far everything is fine. I am taking a relaxed approach I am expecting training to take longer, but I am starting firmly and being consistant because at the end of the day a well behaved dog is a joy to have.
I also discouraged all my puppy owners not to take 2 siblings at once and pointed out the pros and cons of 2 pups together.