i am working on a two factor authentication plugin using a third party API. API and WordPress plugin setting page are ready. now i need break default WP login process in two parts like this:

This is duo WP plugin.Some of my queries:

1. how to break login process in two part and redirect on screen 2.

2. How to use this only for selected user role only.

3. on successful authentication login else redirect back.

any suggestion/help would be appreciate.