You need the convert post tpye plugin. But it will not do the job since all the posts will be converted and since you want each post to be place in respectivie minisites there is another type converter plugin which allows you to convert the post on each individual post and it will take a lot of time if you have a lot of posts. And do back up before making those conversions.
HI buddy ... from original site i can export every category so i think can be more simple. The plugin convert post type i can found it in the wordpress directory?
You can Add this plugin by searching it in your wordpress plugin search bar.