Hi
It's not quite as straight forward as that. Bands earn money from a number of income streams, as do songwriters, each with expected overall percentages going to the band or songwriter. Additionally the people in the band could have completely different roles in the band. Each role tends to have different primary sources for income. If someone performs multiple roles they get their share of each income stream.
For example: A songwriter would expect 50% of the publishers income in a "catch all" agreement. A band member will not necessarily get any income from this. Each performer gets income derived from performing rights (radio performances etc), and income from mechanical rights (cd sales etc). If they are a session man tey get paid a fixed rate, if they perform live but aren't involved in arranging songs they get a percentage of tour income, if they are involved in arrangement they get money from that, if they wrote the song they get money from that.
As you can see, it can get quite complicated.
A great deal depends on what the band agrees. i.e who wrote the song? who arranged the song? who just plays the song? Some bands agree to split everything down the middle where everyone had an equal share in writing and arranging. The same with songwriting partnerships. But this doesn't always work. Some band members write more songs, some just like playing, others like to be involved in promotion and publicity, others like to get drunk,, get the women and do none of the work.
Often we need a better division. If you can agree the roles ovreall, and for each song, the commission shares are pretty easy.
In bands I have been in I have been the main, or only songwriter, writing both words and music and arrangement. In this case I have been the only one entitled to the songwriters share of publishing income. In others I have been the writer and shared the arrangement, or written music for someone else's lyrics. It varies.
Knowing what roles I played allows me to easily work out what I am entitled to.
Cheers
John