Don't see this anywhere in the rules.
How does AI handle group firing? Can it group fire?
If so, does it ALWAYS group fire if possible, or are there specific triggers?
For that matter, can the AI group move?
If a Command Order Card instructs the AI to fire, it will always group fire if it can. this has been covered in previous threads e.g.: https://boardgamegeek.com/article/21773665#21773665.
AI will group move if the card tells it to do so (there are some AI Order Cards that instruct AI to group move).
You can also download the latest Eastern Front rules from academygames.com. It has updated rules (nothing dramatically different from the printed version), and includes Group Attack as the default AI Command Order attack type.