All the questions are related to the .NET framework but not to the .NET Core. I am looking for how to get the all users information from AD group in NETCORE.
If you only plan on running your application in Windows, you can add Microsoft.Windows.Compatibility to your project from NuGet, which includes the System.DirectoryServices namespace, so you can use DirectoryEntry/DirectorySearcher or the AccountManagement namespace like you can in the full .NET Framework.
But if you plan on running this on other OS's, then I think the only option is Novell's library, as Steve mentioned in his answer.