Sorry your post is a bit confusing.
If your brother was the family organizer or a family sharing group and had a Apple Music Family Plan he was sharing with you but then either changed the Apple Music Family Plan to an individual or entirely disbanded the Family Sharing group, then you no longer have access to Apple Music.
If he joined a different Family Sharing Group, then he can't create, join or re-join another Family Sharing group for a full year, and there is no way around it.
One of the other members would need to create their own Family Sharing group and invite the rest of the members to it. Your brother will likely not be able to join though until the year is over. You can only change Family Sharing groups once a year and there's no way around this.
click here ➜ How to set up Family Sharing on your iPhone, iPad, or Mac - Apple Support
If he simply changed the Apple Account he was using when he created the Family sharing group and replaced it with a different one on his own device, then the Family Sharing group would not have been disbanded, nor would you have been kicked out.
You need to really clarify what he did exactly, and what exactly is asking he wait a year. But it sounds like it may be something that cannot be fixed on his side.