All performers should go in the performed by field even if they have other roles in other fields. It's possible for the same person to have multiple roles (
here, for example). Don't put anyone in the composed by/arranged by fields (or any other fields, really) unless you have confirmed proof that they belong there.
EDIT: Just looked at the album more closely and I can see where the confusion arises. Given the names involved, I would assume these are all composers of the tracks but without direct confirmation it's tricky. The album description itself isn't helpful and even has some wrong/misleading information:
Quote:
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Manami Matsumae is the composer on Mega Man 1 and 2
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As if she was the only one responsible for MM2 (she only did one half of one track)