I'm using Windows 10 Pro here, but yours should work the same. If you've got a bunch of computers, all on the same workgroup, do the same for Windows 10. It's not a requirement to use "Homegroup".
In addition, when sharing out all files, folders, and printers on the various computers, it's best to create an admin user on ALL of the computers with EXACTLY the same username and password, login to all those computers with that same admin username, then create the workgroup and share out things.
To create a workgroup on Windows 10, Open the Control Panel, then "System", then select "Advanced System Settings", then select the "Computer Name" tab. Once there, click on the "Change" button to "Rename the computer or change it's domain or workgroup". At the next page, place a dot/tick next to "Workgroup" and type in the workgroup name, then click on OK. It should now be connected to the same workgroup as your XP machines.
Hope this helps.