wordpress user accounts sync our website user accounts development and consulting

We have a wordpress website and membership plugin installed. We need an expert to help us wordpress user accounts sync our website user accounts when user login. The process is like this: 1. visiters come to our wordpress website, and click login button 2. the visiter will be forward to our own website's login page to login or register (we hope users only login and register on our own website instead of wordpress system) [login to view URL] the user login or register, they would be forward back to wordpress site to continue brower our content (mostly education videos) 4. when users login or register on our website, there is an user level in our own system, this level need to come back in wordpress and to change the user membership levels in our wordpress plugin (paid membership pro) so that some video content is only accessable for a specific level of users in our system. 5. our own website system will be developed by our tech team, the 3rd party developer will not have the access to our own system, but only have access to the wordpress site, so you need to consulting with our tech team to get it done Please provide a general solution about how will you get the job done, we review each solutions with our tech team to check when one is the most effective and safty one