Only with the help of a specialised tool that converts multiple OST files simultaneously is it possible to get rich results when converting an OST file into PST format. The best alternative for you is the ZOOK OST to PST conversion programme. Try the demo version for free.

https://www.zooksoftware.com/ost-to-pst/
https://www.zooksoftware.com/blog/import-ost-to-windows10-mail/
https://www.zooksoftware.com/blog/import-ost-to-gmail/
https://www.zooksoftware.com/blog/import-ost-to-thunderbird/