If both users are using the same profile, then a transfer to new PC will handle for both. Here is the link for moving a profile in Windows when installed in default location:

https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer

here is the info in brief steps:

1. ensure thunderbird is NOT running on old machine
2. enter %appdata% in search window on task bar and press Enter key
3. this should open windows file explorer in Appdata\roaming folder
4. highlight the Thunderbird folder and copy to external media
5. ensure thunderbird is installed on second computer and NOT running
6. enter %appdata% in search window on task bar and press Enter key
7. you should be in Appdata\roaming folder , copy&paste the exported Thunderbird folder there. This will prompt to overwrite an existing folder of same name. allow it
8. start thunderbird and all should be there

To be sure your old pc is running a current version, click help>about to see version number

Thanks for replying. We are two separate user names with two separate Thunderbird email accounts. Sorry....I'm a bit of a computer idiot here. Would we be sharing the same profile?

If you log onto the same desktop icon, you're sharing the same profile. You can verify that by clicking the 'account settings' link and looking in left sidebar. My guess is you will see both accounts listed. If not, let me know.

We log on separately...his side and my side of the computer so to speak. We have separate desktops.

OK, I think I know your setup, but it's worth verifying first. I ask each of you to do this: - click help>troubleshootinginformation - scroll down to 'profile folder' and click 'open folder' - write down the location of the profile, e.g., ..appdata\roaming\thunderbird\profiles\<yourprofilename> - if both of you write down either the exact profile name OR everything matches up to the profile name, then my above instructions work for you both. That is, you are either sharing one profile, or you each have a profile within the profiles folder. Either works.

I infer that by 'separate desktops', you mean each of you have a separate desktop icon to invoke thunderbird. I suggest rightdlicking on each icon and writing down exactly what is there to simplify yoursetup on new PC.

I checked troubleshootinginformation and we have two separate profile folders. I'm assuming I need to establish our two profiles on the new computer before moving anything and then moving our profiles individually. Sound right to you?

NO. If they are both in the appdata\roaming\thunderbird\profiles folder EVERYTHING will transfer with the instructions I gave previously. What you describe is a normal structure.

Okay, here's what I've got:

C:\Users\Glenn\AppData\Roaming\Thunderbird\Profiles

    and

C:\Users\Eddy\AppData\Roaming\Thunderbird\Profiles

Don't I need to move these separately to the new computer? Not understanding how everything will transfer if I only move one of them.

Really appreciating your assistance here...

You are correct. You each have set up different Windows ID, so each of you need to do exactly as I documented, but within your own windows setup. Thanks for the feedback.  :)

Thank you for all your assistance!

I was glad to assist. :)