They are not ready, what the older chin is doing is showing dominance. You need to be 100% sure before you put them in a cage together. Not to sound bad, but it can take a matter of seconds for a chin to kill another, let alone an adult and a 10 week old kit. You need to take your time, it could take up to a few months or well, it could be never. You start with mutual play time, when there are no scuffles anymore, you can move to supervised visits to each's cage. A little bit at a time, not just throw them in and hope all goes well. Once you have been doing that for a time and nothing ensues you can try a longer visit, a half a day or such, once your COMPLETLY confident you can try an over night, just remember not all chins get along and you need to remember your there to protect them no matter what. Take your time and dont rush, from the sounds of it they are not ready, its a long process trust me, i had a pair that took 2 months. Now they cant be seperated. : )