how do I sync all my devices together on one library

Greetings georgefromst.petersburg,

If you are wanting to sync your content from a computer, use the steps included in the related article above your post. If you want to have that content update automatically, follow the guidance found here:

Access your music library on all your devices - Apple Support

Take care.

You can sync multiple devices from a single library. Each gets its own selection of synced content which it remembers. If you have content on any of your devices that isn't in your library see See Recover your iTunes library from your iPod or iOS device - Apple Community.

If you have multiple libraries that you want to gather together you can export one library as an XML file and import file that into your main library, then consolidate and dedupe. Repeat for each additional library. See Duplicate songs in iTunes/Music - Apple Community for advice on deduping.

tt2