How to get groups members in sdl tridion using core service in c#

Question

I trying to get the group members from cms. I have tried this code it gives all users how to get the group members. I want to get the members from the admin group I know the tcm id tcm:0-2570-61168

                   var users = basicClient.GetSystemWideList(new UsersFilterData {
                BaseColumns = ListBaseColumns.IdAndTitle, IsPredefined = false });

also tried this code

var targetType = basicClient.Read("tcm:0-2570-61168", readoptions);

the above code returns the groupdata object with no any getmembers method

I want to get all members from a given group and remove specific user from that given group