
I would say that a pup of 9 months isn't really yet old enough to really be thinking in terms of territory and dominance yet, though of course he is at puberty and may act out like a teenage oik, as she hasn't the maturity, so this is where care needs to be taken. I would imagine that he is most likely to forget all about you and be pleased with a new playmate. You will need to ensure he doesn't overtax the pup, and vice versa pup doesn't overstep the mark making immature young man over react.
Your biggest problem is likely to be is that you may become pretty superfluous to the pups if your not careful as the company of their own species, someone that speaks their language likes what they like and plays like a dog is going to be some competition for their attention.
This is why you will need to do a lot of training with them seperately to get a real bond with them.