This website gives a complicated answer:
Composer
The composer field is where things get a little more tricky…
Performance Rights Organisations
The composer name is usually the legal name of the credited writer(s), not the artist alias they perform under.
Some writers decide to exercise their moral rights to be credited for works under a pseudonym.
This depends what name you have registered under with your Performance Rights Organization (PRO).
You will typically credit every writer involved. Also, the percentage of credits they have for the composition and all of their PRO identification numbers, known as CAE/IPI numbers.
This should be relatively simple if you’re signed to a PRO. Your ID number will be available to you from their site or in their correspondence.
Getting an ID number from other artists can be trickier.
Collaborations
In the instance of any collaboration, you should always fill out a split sheet with your collaborators. With this, you agree to the splits of the ownership of the song and take note of your collaborators PRO CAE/IPI numbers.
If your collaborator isn’t registered to a PRO, you can leave that out in the song metadata. – But, always outline the credit split.
Your Composer metadata should look as follows:
“Elliott John Gleave (50%) (PRS #00045620792) / Jimmy Rick (50%) (PRS #00045620793)”.
If there is another writer:
“Elliott John Gleave (33.33%) (PRS #00045620792) / Jimmy Rick (33.33%) (PRS #00045620793) / Tim Burtford (33.33%) (PRS #00045620793)”.
The percentages should reflect whatever was agreed upon between you and your collaborators.