Let's start with this. The pagerank, authority and the positioning of the URLs in search page results belongs to each individual blog. yes you can import content from one blog into another and yes you can delete the blog it was originally in. Doing that means all the content must be re-indexed by search engines and start over again from ZERO.
The next thing to be mindful of is that after you delete the original post those deleted pages will still appear in search engines for at least 3 - 6 months and when clicked on they will be broken links so the visitors will experience a 404 (page not found) error.
To export and import. If you already own the blog, please follow these steps:
Log into the old blog, go to Tools → Export, and download the XML (WXR) file to your computer.
In the new blog, go to Tools → Import → WordPress, and upload the file you downloaded in step 1. After you upload the file, you can choose the option to Download & import file attachments if you want to move your media files.