Sharing Credit

I'm just wondering what peoples opinions are in regards to sharing credit on songs.

Just a few instances..
If you write a song and the music is all yours, you've written the chorus for the song but somebody else comes up with a first verse that takes you in a different direction. They also sing it. How would you credit that person?
Would they be entitled to a share of the royalties if the song made any money?

What about if you work with a singer and they mostly just do vocals, but occasionally they inspire you to write songs a certain way to suit they're vocals?

How would you handle it if you wrote a song and advertised for a singer online. Somebody answered your ad and did the vocals for you but you've never actually met them in person. Nothing was discussed as far as payment or anything. Then a year later, the song becomes a hit. How would you credit the person and would you owe them any money? If so, how much?

Short cold answer...if theres no contract,its all up for grabs.

The music and lyrics I write for my band is done all by me,but I feel like a jerk saying "my song/s" e.c.t,so I credit the rest of the band just to be nice saying "our song/s" e.c.t.
I'm nobodys superior in the band and would like to shift the process of writing material into a group effort.
We could sit around all day and jam randomly,but that will get us nowhere...we need group brainstorming sessions.

I'm way of the subject...

Later! \m/