I need someone to help me place my hands on some legal release forms for Music.

Most music is being written especially for the film.
Some will have vocals recorded on top by our lead actors.
And only one song has been previously recorded by someone, but they have agreed to let us use it.

I feel like all three of these statements should have something to do with the kinds of releases I need.

Help, please!
I really just need something simple and not intimidating that people will not be afraid to sign.

Thanks!