What if I co-wrote a song with someone else? Do we both need to become Members of The MLC?

The answer depends on which parties have the right to register the co-written musical work with The MLC and collect the mechanical royalties. If co-writers create a legal entity, which they co-own, and which has been assigned the right to register the co-written musical work with The MLC, and collect the related mechanical royalties, then only the legal entity needs to become a Member. If each co-writer has retained their right to register musical works with The MLC and collect their own mechanical royalties, then each co-writer needs to become a Member of The MLC.