Integrate stand alone PHP dynamic website and wordpress blog

General information for the website: We are a dynamic website!
Description of every page/module: We have a PHP website, that allows users to register and login. They have individual dashboards with information personal to themselves. We would like to give them access to create blogs that can be displayed on their profiles. Our primary domain is using core PHP and our secondary sub domain is on wordpress purely for blogging. I would like to include the following features:

1. New users get registered on both our primary and secondary website
2. when a user clicks on create a new blog within the primary website, he/she should be able to create the blog from the wordpress create a blog page within the secondary website.
3. blogs to be displayed within the secondary domain
4. Individual blogs displayed on the secondary domain, should be displayed within the profile's of authors using the primary domain.
Description of requirements/features: I have been able to complete functionalities between 1, 2 and 3. I need help with the 4th functionality. Let me know, if this is something you will be able to do?
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