Appropriate license for songbook shared with friends

Question

I am planning to write a songbook (LaTex, Lilypond) of christmas/seasonal songs and am looking for the right license to pick. Some parameters of the project:

• The book currently is planned with songs in the public domain
• I am toying with the idea to include songs from other open-source projects with free licenses (like Unlicense)
• I might slightly alter some songs (at least the chords)
• The book will be collaboratively created between me and some few friends
• I am planning to place the contents in a private github/gitlab repository
• The book will not be published freely, only a few copies for the collaborators will be created
• The book will not be used for public singing, only for domestic music

I have the following questions:

1. Do I need to pick a license, if I don't plan to publish the book?
2. What would be a good license?
3. What happens, if I don't pick a license?
4. What happens, if I want to include non-free songs?

Answer 1

1. Do I need to pick a license, if I don't plan to publish the book?

No.

2. What would be a good license?

A Creative Commons license is appropriate for non-software works. Use their license chooser to choose a CC license.

3. What happens, if I don't pick a license?

All rights reserved.

4. What happens, if I want to include non-free songs?

You have to ask for permission to the song's copyright holders first if you'd like to distribute the song with the song book. Merely linking to the song on YouTube or another site is okay.