Hello and welcome to Binky Bunny! I assume that your bunnies aren’t spayed since they were only 3 months old when you got them. It doesn’t matter if rabbits are siblings, once they hit puberty, which can start around 4 months of age, they can start acting aggressive or territorial, and that can lead to fighting. Rabbits can severely injure each other when they fight, so you will need to keep them separated until they have been spayed and recovered from the surgery, then you can start rebonding them. Sometimes rabbits just don’t get along and have to be kept separately their whole lives, but that isn’t very common.
You may need to take your bunnies to the vet to get their nails clipped since you are having trouble with that. They shouldn’t charge too much for it. Before they need clipping again, you can look at videos or read some articles about the various ways to clip nails, then try again yourself.
You can find a lot of good info on this site and feel free to ask any questions you may have about rabbit care.