I want to get the List of all users inside a Group in my code, is there any Repository that can provide me with that information.
Is it Roles or Visitor Groups that you mean?
For users in Roles (admins, editors etc) try something like this:
private readonly Injected<UIRoleProvider> _roleProvider;
Then use the method "GetUsersInRole":
var groupName = "WebEditors";
var userNames = _roleProvider.Service.GetUsersInRole(groupName);