As we know, Outlook doesn't offer a way to open EML files. If you want to convert your EML files into Outlook PST format then, you can take help of any third-party tool, I would like to suggest try
EML to PST converter tool from Shoviv that can export your multiple EML files directly into PST outlook format regardless of any issue. It supports various email clients where EML files are generated such as Thunderbird, Outlook Express, Windows Mails.
Download this tool from here:
EML to PST Converter