How to get the users in a group

I would like to write a function that given a name of a group returns the usernames of the users that belongs to that group.

If I have a group named “Members” and “Tom”, “Tim” and “Theo” is part of that group I would like to have a function that looks somthing like this:
I am a C# developer not a PHP developer

string[] GetUsers(string groupName){
find the groupId mathing the groupName;
return all userids that is member of the group found.
}

Where the returned values are “Tom”, “Tim” and “Theo”.

How to do this in PHP using this plugin.
I like the possiblility to create groups of users that this plugin gives and I think that it can be used in other functions outside this plugin.

https://wordpress.org/plugins/contexture-page-security/