Ipad Storage

You can use iCloud Music library to stream your music. It will use some space while streaming, but should be released after you are done playing back the song.

Turn on Sync Library with Apple Music - Apple Support

Do note you will require a constant internet connection for this.

You need to delete them from iPad, so they show a cloud icon. Turning on won't remove them from the iPad.

If they don't show a cloud icon on the corner, then they are still on the iPad.