How to add security group from another domain into Servers Local Administrator group's domain ?

Follow the steps in this article. You can use GPO Local Users and Groups preferences
https://www.experts-exchange.com/articles/29596/Securing-Active-Directory-Administrators-Groups.html

Hmm, if i am not allowed to create GPO ?

Do you have an account that is member of the local administrators group on all the servers?

If you want to use Powershell then use this one from the Microsoft ScriptCenter Gallery

###################################################################################### 
#             Author: Vikas Sukhija 
#             Date:- 08/30/2014 
#              Description:- This script will add user to local admin 
#                       on remote server.  
###################################################################################### 
 
#############ADD GUI Component###################################### 
 
function button ($title,$domain, $user, $Server) { 
 
[void][System.Reflection.Assembly]::LoadWithPartialName( "System.Windows.Forms")  
[void][System.Reflection.Assembly]::LoadWithPartialName( "Microsoft.VisualBasic")  
 
    $form = New-Object "System.Windows.Forms.Form"; 
    $form.Width = 500; 
    $form.Height = 150; 
    $form.Text = $title; 
    $form.StartPosition = [System.Windows.Forms.FormStartPosition]::CenterScreen; 
     
    $textLabel1 = New-Object "System.Windows.Forms.Label"; 
    $textLabel1.Left = 25; 
    $textLabel1.Top = 15; 
 
    $textLabel1.Text = $domain; 
 
    $textLabel2 = New-Object "System.Windows.Forms.Label"; 
    $textLabel2.Left = 25; 
    $textLabel2.Top = 50; 
     
    $textLabel2.Text = $user; 
 
    $textLabel3 = New-Object "System.Windows.Forms.Label"; 
    $textLabel3.Left = 25; 
    $textLabel3.Top = 85; 
  
    $textLabel3.Text = $Server; 
     
    $textBox1 = New-Object "System.Windows.Forms.TextBox"; 
    $textBox1.Left = 150; 
    $textBox1.Top = 10; 
    $textBox1.width = 200; 
 
    $textBox2 = New-Object "System.Windows.Forms.TextBox"; 
    $textBox2.Left = 150; 
    $textBox2.Top = 50; 
    $textBox2.width = 200; 
     
 
    $textBox3 = New-Object "System.Windows.Forms.TextBox"; 
    $textBox3.Left = 150; 
    $textBox3.Top = 90; 
    $textBox3.width = 200; 
     
    $defaultValue = "" 
    $textBox1.Text = $defaultValue; 
    $textBox2.Text = $defaultValue; 
    $textBox3.Text = $defaultValue; 
     
    $button = New-Object "System.Windows.Forms.Button"; 
    $button.Left = 360; 
    $button.Top = 85; 
    $button.Width = 100; 
    $button.Text = "Ok"; 
     
    $eventHandler = [System.EventHandler]{ 
    $textBox1.Text; 
    $textBox2.Text; 
    $textBox23.Text; 
    $form.Close();}; 
 
    $button.Add_Click($eventHandler) ; 
     
    $form.Controls.Add($button); 
    $form.Controls.Add($textLabel1); 
    $form.Controls.Add($textLabel2); 
    $form.Controls.Add($textLabel3); 
    $form.Controls.Add($textBox1); 
    $form.Controls.Add($textBox2); 
    $form.Controls.Add($textBox3); 
    $ret = $form.ShowDialog(); 
    return  $textBox1.Text, $textBox2.Text, $textBox3.Text 
} 
 
$return= button "Enter Parameters" "Enter Domain" "Enter User" "Enter Server" 
 
 
 
### Add Prameters returned from button  
$Domain = $return[0] 
$UserName = $return[1] 
$Computer = $return[2]  
 
## USe ADSI to connect to Remote Administrators group 
 
$Group = [ADSI]"WinNT://$Computer/Administrators,group" 
 
$User = [ADSI]"WinNT://$Domain/$UserName,user" 
 
$Group.Add($User.Path) 
 
if($error -ne $null) 
 { 
  (new-object -ComObject wscript.shell).Popup("$error",0,"Done",0x1) 
 } 
else 
 { 
 (new-object -ComObject wscript.shell).Popup("Operation Completed",0,"Done",0x1) 
  } 
 
##########################################################################################################

Select allOpen in new window

https://gallery.technet.microsoft.com/scriptcenter/Add-User-to-Local-964db4d0

Hmm, those script are asking to enter the servers manually. I need to query for the servers, read them and add the OtherDomain\Domain Admins into the "Administrators" local group of every server automatically.

Just checking...
Why not add OtherDomain\Domain Admins into Domain\Administrators group?

Hmm don't follow.... Domain\Administrators where ? In the domain controllers of the domain ?

There is a group called Administrators in both domains. This group is a Domain Local group.
There is a Domain Admins group in both domains. This group is a Global Security group.
You should be able to add Domain Admins from one domain into Administrators group on other domain.
This way you will have Administrators rights with Domain Admins to other domain's devices

Yeah, but that does not alleviate my RDP problem on every server in that domain. Remember there is Domain1\Domain Admins and Domain2\Domain Admins. Domain2 has bunch of servers. Those servers have "Administrators" local group. In order for me to RDP I have to add the Domain1\Domain Admins into the "Administrators" local group to every server in the domain2. Thanks,

That is incorrect. Domain2 domain Administrators group has Local Administrators rights on all Domain2 servers explicitly

Maybe, I am not following you. The attachment is domain2. Where do you want to add the Domain1\Domain Admins group to ?
Screenshot_5.png

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Accept: SquigglyMonkey (https:#a42446475)

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