different number of songs appear on my 3 computers with home sharing

There's a few different things going on here. Starting with this one:

But, I noticed that when I turned off the main computer with the songs, then everything disappeared off one of the other computers.

Was the one-of-the-other-computers the computer which has no music stored on it locally? If so, that's what you would expect to see if you were streaming music to it from a different one, and then turned the different computer off.

Or was something else going on?

Should I copy the music library to each computer?

That might be the way to go. You can use home sharing to shift the music about (while you're on the same network), as per the following instructions:

HT2729 Re: How can I merge my itunes music library from two different computers

Getting the playlist information across to the other computers (so it's available locally) is a bit less straightforward, but still doable. (I've done it.) See the instructions in the following post for that:

Re: transfer playlists to new computer

Doublechecking a couple of things, Anita:

On my desktop computer I have all my songs under ...Anita's Music. My husbands songs are on the same computer under ....Ray's Music.

How are you doing the demarcation? Are these two different playlists in a single library, two different libraries in a single Windows user account, or different libraries in two different Windows user accounts?

What kind of iPod do you have? (Touch, nano, shuffle, Classic, or an older model?)

🙂 many thanks.

I'm going to try flagging down an iPod Touch specialist and get them to come have a look at this. (The ancient noir-household iPod Touch 1st gen is with Helen up in Wellington at the moment, so I think it's prudent that we get someone in who's more up to speed and has the right-kit available for doing this on a $th gen.)

I have different iOS devices (an iPad & an iPhone) but the principle is the same.

I'm assuming for now that you can see your playlist in iTunes and that you have already added the extra music you want to it...

When you connect the device to iTunes you can select the device in the left-hand column. This then leads to a tabbed display allowing you to adjust what will be put on the device. On the Music tab tick Sync Music, below that use the option Selected playlists, artists, albums, and genres. In the Playlists section below that tick the playlists you want on your device and untick those that you want to remove. You can repeat the selection process for other media types. When you are happy click Sync in the lower right-hand corner and your device will be updated.

tt2

b noir has flagged up an issue I may have overlooked above.

Re-reading the thread it seems that there are two independent libraries (now essentially replicated on three machines) each holding either your content or your husband's, but with both sets of media added to the one iPod touch. Is this correct? It makes my suggestions earlier somewhat wide of the mark.

It might help to determine if the device is set up for manual management or automatic syncing. When the device is connected to iTunes select the summary tab and scroll down. If there is a tick against Manually manage music and videos then it is set for manual managment. In this case you can update your playlist on the device by dragging the playlist in the left-hand column onto the device in the left-hand column. Any new tracks will be added to the device and the playlist updated.

tt2