I know that rabbits of that age can have unlimited pellets, usually alfalfa pellets, but it is possible to overfeed pellets, so you shouldn’t refill their bowl if they empty it over and over.
Since they are 9 weeks old, you will have to separate them in a couple of weeks, before puberty sets in. It doesn’t matter if they are sisters, once they start dealing with hormones, there can be aggression and fighting and injuries. You can keep them near each other in the same room, but they shouldn’t have any physical contact when they reach 11 weeks old or so. They will have to take turns coming out for play and exercise. Then after they are spayed and a few weeks have elapsed for the hormones to die down, you can start bonding.
Babies can be friends, but they can’t truly bond until they are older and have been spayed or neutered.
Edited to say that I was typing and didn’t see Azerane’s post. I didn’t mean to duplicate it.