Pro Cloud Server

It is standard Microsoft Windows Service, that manages a pool of database connections for each defined repository. It is designed to run on your hardware, so that you have full control of how it is configured and who has access to it and more importantly your data remains totally in your control..

EA clients do not require PCS tokens in order to access PCS based repositories.  Therefore being a licensed user of EA client is not relevant when it comes to WebEA.  In web browser environment the concept of a licensed user (or machine installation) does not exist, instead it is based purely on browser sessions.  ie each browser session that logs into a WebEA repository consumes a PCS Token.  This means that a single user/machine with 3 different browsers (Chrome, Firefox, IE) and if each browser that logs into WebEA would consume a token. 3 browser sessions would mean 3 tokens.
Regardless of where users comes from (Azure DevOps or a plain browser) a licence or token would be consumed.

Note: EA clients do not require a PCS licence to access PCS-based repositories.  Conversely, no EA licence is required to use WebEA.

ProCloudServer is also used as a gateway for third party providers, in the excerpt here.
So to summaries, with one Token you can have :
- Up to Seven repositories with Pro features enabled
- One External data integration
- One  WebEA, Prolaborate and OSLC user
at the same time

There are Unlicensed, Token, Team Server up to the Enterprise Edition available. Compare the functions in the Feature Matrix

Prolaborate

lets you Share, Visualize, and Analyze information from your EA models and publish them in knowledge management apps like Confluence, SharePoint, etc. It also lets you Collaborate with business and non-EA users, and Integrate with tools like Jira and Azure DevOps.
NOTE: The Confluence integration allows the shared diagrams to show live information all the time without manual intervention. Any business user(Confluence user) can view and publish information from the EA models easily with a few clicks. They need not have any licenses for other apps. Thus, the Confluence integration does not consume a Prolaborate license.
A license from the Pro Cloud Server is also obligatory for the use of Prolaborate

"Licensed Users" denote the total number of users you can add to Prolaborate; Only the users who are added can participate in reviews, discussions, edit information, create dynamic visualizations, analyze information, and work on all the features of Prolaborate.They are neither floating nor named. As they are not named, you can easily remove and add users as needed.Read more in the Forum.

There are Growing (up to 49 users), Large (up to 1500 users) and above the Enterprise Team Edition.
In the Growing Edition, all integrations, Open Community Access and Single Sign-on (SSO) are available for an additional charge for 10 licenses or more.
Team Edition includes Open Community Access;Single Sign-on (SSO), Open Community Access available at additional cost
In the Enterprise Team Edition are all integrations included.