Ten weeks is a little earlier than usual, but perfectly possible. Pied's aren't smaller generally, but robos can really range in size. My boys have 14g difference between the heaviest and lightest. My girls nearly as much.
Get them sexed as a priority, if you're not confident yourself, take them to your local vet. They cold well both be boys, but if they're not obviously you need them apart as soon as possible.
Have you got everything set up to give them the best chance possible? Two of everything, an open nest, no levels to claim dominance over, scattered food?
It's good that Pip seems fine with it all, look out for him not eating, changes in weight, changes in fur condition if he stops grooming, sleeping apart as he's not allowed in the nest, keeping to the edges of the cage, dashing quickly from covered areas. Look out for tufts of fur missing from his bum as that's the usual first attack area, and keep an eye out under the fur on the bum as often the first little nips you wont see, but it will be building into a bigger attack which obviously you want to avoid.
Have you another cage ready should you need to separate? As Pip seems relaxed so far it's nothing more than a display of dominance which Pip is unbothered by, and as long as none of the signs I've mentioned are present, I actually wouldn't separate yet, but keep a very very close eye on them.
Just make sure Pip isn't a Pippa first
