MS Planner & MS Project

Hello, I work as a project manager, and we want to use MS Project in the company. However, it seems to be not very user-friendly. How can I import a project file that has already been created in the MS Project Desktop version into the Project Web App (PWA) with all resources and tasks included? Even though I import the file, it does not show up in PWA, but newly created projects do. Another question is how to send email reminder notifications for tasks assigned to colleagues in PWA. Is it possible to work with both Project Online and the desktop versions simultaneously, meaning will the entered information be updated directly in the other version? Can someone help me please.