All songs written and arranged by (band name), based on material composed by (one of the musicians in the band).
Would that make the composer be the band or the musician? I opted for the band, but asking here just to be sure. I have not found another way to enter this kind of info. If there is I’d be happy to add it of course.
Based on that text I’d probably add “(one of the musicians in the band)” as the composer and “(band name)” as lyricist on the Work and also put “(band name)” as the arranger on the Recording (if it’s a popular music or similar recording).
The lyrics are specified separately so that part is easy and I already added the band as the arranger.
I’m going to use both the band name and the separate band member for composers and add a notation.