It’s always better to keep bunnies inside the house, where they are part of the family. Even though the bunnies are in a garage and may be protected by weather extremes, parasites, predators, etc., it is still not as good for them as being in the house with you.
You will have to bunny proof any rooms or areas they are in when they have out of cage time for play and exercise. Go to the BUNNY INFO link at the top of the page here to see information on bunny proofing as well as info on housing, feeding, bonding, etc.
At 8 weeks of age, you will soon need to separate the bunnies. Even if they are both female (and sometimes they are mis-sexed which leads to unplanned litters) they shouldn’t be together once they start into puberty, which could be around 12 weeks of age. With the hormones that puberty brings, you can have territorial feelings and aggression, which can lead to fighting. If rabbits fight, they can severely injure each other. It doesn’t matter if they were related or litter mates, they need to be separated by the time they are 12 weeks old. They shouldn’t be housed together and they shouldn’t be out to play at the same time. They can stay in the same room, though. After they have been spayed and a few weeks have elapsed, you can start the bonding procedure. They only have a temporary baby bunny bond now.