Setup an Outlook rule on each account to copy/move incoming emails to a central Inbox -
You really don't want to move imap mail into a pst - if you copy, you end up with duplicates; if you move, it deletes from the server - you'd be better served by removing the imap account and using pop3.
it's better to use instant search to create the unified inbox. you can do this with simple search terms: folder:Inbox received: (this week) or you can use a macro to automate it.
https://www.slipstick.com/how-to-outlook/how-to-create-a-unified-inbox/