If you are experiencing issues with Multiplayer games not working.  There is a workaround for this problem.  

Set your exe file to Windows XP SP3 Compatibility mode and setup a multiplayer game via GameRanger as per normal - http://www.gameranger.com/

You can do this by locating the exe file (default locations listed below) and following the additional instructions. 

1. 
 C:\Program Files (x86)\Steam\steamapps\common\Stronghold 2

 C:\Program Files (x86)\Steam\steamapps\common\Stronghold Legends

2. Right click and select Properties.

3. Click on the Compatibility tab.

4. Tick 'Run this program in compatibility mode for:'

5. Select 'Windows XP (Service Pack 3)'

6. Click on OK.

7. Run GameRanger and either Host or Join a game.