Q: how do i sync iTunes between different macs

Hello, Tienie1968!

The Automatic Downlod functionality of iTunes should provide this.

iTunes Store: How to enable Automatic Downloads

http://support.apple.com/kb/HT4539

Enabling Automatic Downloads on your computer

1. Open iTunes.
2. If you have not already, authorize your computer for use with your Apple ID by choosing Store > Authorize This Computer. See this article for information about iTunes Store authorization.
3. For Mac computers: Choose iTunes > Preferences and click the Store tab. 
   For Windows computers: Choose Edit > Preferences and click the Store tab.
4. You can enable Automatic Downloads2 for Music, Apps, or Books under "Automatic Downloads."

Note: If the checkboxes are not selectable, you will need to sign in to the iTunes Store with your Apple ID.

Best regards,

Allen