To Merge Outlook data files into one PST files then I would suggest the KDETools PST Merge. It joins various PST files such as Emails, Calendars, Tasks, Notes, Contacts and all. Merge PST files without any duplicates PST files. It joins PST files in all Version of Outlook and Windows. Consolidate multiple PST files without installing of MS-Outlook. Join various PST items with demo version is also available. Merge only selected PST files with date ranges.
More Info: https://www.kdetools.com/pst-merge.html
Combine Outlook files with all data or selected data with Merge PST Tool in just 4 simple steps. I have used this application a week ago and got fine results therefore, I would like to suggest you to use this application to merge Outlook data files into one PST file. It help you to join PST files without Outlook installation.
Visit here for more info: https://www.osttopstapp.com/pst-merge.html