Rest Api Extract Users In Group Roles

Hi, what endpoints do I need to extract all users in a group that belong to a certain role?

I have tried the following endpoints with no luck:

/api.ashx/v2/groups/{GroupId}/members/roles.xml?MemberType=users

This is returning 0 results.

/api.ashx/v2/users.xml -> /api.ashx/v2/roles/user/{username}.xml

Here I am getting all users then looping through each user and checking their roles permissions however this is not returning expected results. 

Any help would be appreciated!

Thanks

For example, I need to get an extract of all users within a group. The extract must contain "Username, Display Name, Email, and the roles they have for that group".

At present, I use "/api.ashx/v2/groups/{groupid}/members/users.xml" to get a list of users for a specific group. How do I then get each user's role in that group?

Membership status firstly and if possible security role

So the roles for a user are not group specific, they are site wide?