You need their p12s and the passwords for them. You can't create your own.
1. In Single edition Workflow, you do not have an option to publish as Public, thus publish as Private then you would need to export the Folio and import it in Viewer Builder while building the App. Use the serial number to activate your build for download.
Read the following link for more on the workflow:
2. Read the iPad publishing guide for creating required certificates (Attached). It's best if you complete the whole certificate process on a Single Mac using keychain Access to avoid complications. While creating certificates, remember to de-select enable for iCloud. I would recommend going though the guide in detail and follow step by step process as mentioned in the guide.
You can create p12 and .mobileprovision through this tutorial
You can directly create a p12 file in the Windows system, do not need to convert, do not need a Mac computer