Hello Christopher
This is why it is so important to understand how Airbnb works before a host dives into listing with them.
When you set up a listing it is always linked to the individual rather than the property. Airbnb states this clearly in their information for hosts. This is the reason why you can't change the listing admin.
If you had wanted the reviews in your name, you could easily have set up the profile in your name, or set it up so that you had four properties each under your profiles. You have now waited a year to do something, so the list of reviews your brother has grows longer and longer.
Unless you and your brother are going separate ways in your business, or you are looking to grow your listing portfolio, it shouldn't matter which brother the listings are set up under.