Male rabbits can actually withdraw their parts into themselves, so it could be when you checked, they weren’t there! Very deceiving rascals…
I agree that both Marshmellow and Oreo (assuming from your username!) don’t seem to have a properly established bond yet. It could be when they were young, they were fine, but now that they are older and the potential of hormone development is ripe, they have become rowdy.
As per the bonding information found on this website, you’ll want to separate them until you can get a confirmation from an exotic vet on them -both- being neutered. If they are not, you must wait until they are to being the bonding process. If they both are already, start from the beginning of the bonding process!
In regards to nipping you, if they are not neutered, they will usually dissipate doing so following a neuter. If they are neutered and nipping you, you can signal to them it hurts by retracting away the body part and letting out a high-pitched “ow” sound— this signal lets rabbits know when they’re hurting each other.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.