Where to get UserList from Web API

Hello 

I am currently automating report generation from ProjectWise for a client of mine. One of the reports contains a list of all users, including the `UserList` they belong to. While I can query most of the user information from the `User` class - and then merge it with more information from a custom user information class of this project - I can't figure out how to obtain the UserList the users belong to. Which class do I need to query? Is there a way of getting the information directly from the `User` class by setting some of the query params to related classes? 

Thanks