Could dynamic content work for you?
If all the workspaces are using 1 partition. How do you distinguish that the lead records that has filled out a form is from a specific region/ child company.
I would suggest using fields to capture information such as
Field - Region that sorts the different regions when someone fills in a form OR when you run a list import
Additionally you can use a field to identify if the record has come through your child company. Either a check box or another field to capture this information.
Then you can use the preference center which would store this value from hidden elements such as If they are filling the form in United States, then the region would be marked as CAM.
If they are filling the from from United States and they are coming in from your child company, then the region would be United States and the child company field would be checked to true.
This would need to be set up on your front end web pages.
Similarly you can use this subset of data to send your email communications. so if child company field is checked to "True" - then send email B which is based off child template version 1
Again this is just a concept which you could use because you could technically set this up in so many different ways.
Hope this helps