
I presume you still have their dam, did she not keep order within the litter or intervene now between the pair? These 2 have had their litter mates leave in the past week so that is a big upheaval for them to suddenly be on their own, did the bigger pup show any really rough play before this week? I don't think seperating them to different rooms will help, they need to see each other and that they are not missing out on anything, they are only 9 weeks old you should be able to discipline them and intervene before it gets into a full on fight,never leave them alone together and praise them when they behave nicely and give a high value treat, cheese works well here.
I have had problems in the past between bitches, they lived together for the first 6 months of the younger ones life then she came to me, 10 months later the other one joined us and everything was great, the younger one was top dog and the other bitch and my male were happy to fall into line with this, 18 months later the older bitch had pups[ I had failed to get the younger one pregnant]initially everything went on as normal then one day they started fighting and it was in ernest, the only blood spilt was mine so I seperated them into a crate with a divider so they could see that neither was getting preferential treatment, things went back to normal again but I was for ever wary especially when they were due in season, they had 3 flare ups and it was the older bitch starting the fights but neither bitch picked on the daughter of the older bitch just on each other, I hope never to be in that position again, I have 2 bitches here now, one is 15 months old and the other one 3 last Xmas, thus far everything has been fine, I worry that things will change when the younger one has pups next year, at the present no one seems to be acting top dog but that may change.
I hope you can sort them out or else you are going to have to rehome one of them for your own sanity if nothing else.