Categories list using rss feed

Hello, spent a lot of time for searching the solution to my task, but i’m unable to find it. So i have 2 sites, first is presenting the company and second is company blog, they are installed on different databases, so i need to get Newest posts, comments, ant categories from blog. Posts and comments are done by using RSS feeds, but the main problem is categories. How to get all the list of categories in the first site from second?