Hello and welcome to Binky Bunny. I assume that you are currently housing your rabbits together. It is recommended that rabbits be separated before they are 12 weeks old. It doesn’t matter if they are the same gender or from the same litter. When they reach the age of puberty, which can start at around 12 weeks, they shouldn’t be together. The hormones that puberty brings can cause aggression and territorial feelings. That can mean fighting. When rabbits fight, they can severely injure each other. They shouldn’t even be allowed out at the same time for exercise.
Right now, they have a temporary baby bunny bond, which is not a true bond. You will only get a true bond after rabbits have been spayed or neutered and have gone through the bonding process. Depending on the vet’s preference, females can be spayed at around 5 or 6 months of age. Then you have the recuperation period, plus you need to wait a few weeks to let their hormones abate before you can start bonding.
If you go to the BUNNY INFO link at the top of the page, you will see a lot of good information on all aspects of rabbit care, including bonding. Here is another article on bonding from the HRS: http://rabbit.org/faq-bonding-multiple-rabbits/
Feel free to ask any questions that you have.