Pine and cedar shavings are bad for rabbits. They contain dangerous aromatic oils. Pine pellets are safe, though, just not the shavings. You actually aren't supposed to have any bedding/litter on the floor of the cage if you are trying to litter box train your rabbits. It is confusing for them. Litter should only be in the litter box. You can put fleece blankets on the floor of the cage to make it more comfortable, but watch out for chewing. You will probably also not be able to fully litter box train them until after they are spayed.
You need to make absolutely sure that both rabbits are females. Many pet store employees or breeders have said that, then you are presented with an unwanted litter in a short while. Sometimes two litters if you didn't realize the female was pregnant and the male was still with her after she gave birth, since rabbits can get pregnant again immediately. Even vets have been known to mis-sex rabbits.
If they are females, you will only be able to keep them together until they are about 11 weeks old or so. When puberty hits, and the hormones come flooding in, there can be aggression and fighting. When rabbits fight, they can severely injure each other. It doesn't matter if they grew up together. Baby bunnies can be friends, but they can't permanently bond until they have been spayed or neutered, a few weeks have elapsed since their surgery, and they have gone through proper bonding sessions.
Here are 2 good articles on bonding: http://rabbit.org/faq-bonding-multiple-rabbits/ http://www.binkybunny.com/BUNNYINFO...fault.aspx
If you haven't already done so, check out the BUNNY INFO link at the top of the page. It is very helpful and covers all the basics of rabbit care. Also, feel free to ask any questions.