Hello @Marco373,
Reviews can't be moved from one profile to another. They belong to the profile owner.
If your brother takes one of the listings to his profile he must start from scratch regarding reviews.
I'm not sure if would be the answer for what you want to do but you could investigate the co-host feature and make your brother a co-host for one listing while you are the only person dealing with the other one. Reviews for both listings would still go to your profile though.
Steve