You can't. A defender may not defend more than two co-defendants. Link to the article: the Supreme People's Court's explanation on the application of Article 38 of the Criminal Procedure Law of People's Republic of China (PRC)?
1. The defendant may entrust one or two persons as defenders.
2. A defender shall not defend two or more defendants in the same case who have not been dealt with in the same case but whose criminal facts are related.