Unable to play while son is in game

[Bhalthazar]

Hello, wanted to see if we set up the games wrong somehow? My son has been playing for a while, and I have just installed the game on my computer. We can each play but not if the other is logged in to the game (we have Comcast to the house and use a router for our computers to get to the internet).

Is there a setting or some other way that we can both play the game at the same time? I was kind of hoping to group with him etc. Thanks in advance for any assistance!