In your Workflow, you would have a different step for each group
Imagine the Workflow kicks off and goes to a transition step:
Group C Review, which would have a group assignment and not a user
assignment. That step has a couple of actions, maybe to send back
for changes and approve to Group B.
From there it would go to another transition step: Group B
Review, which would have the same type of group setup. It could
have a few actions as well, send back to C, send back to owner (the
person that started the Workflow in the beginning), approve to
The main idea is that you'll want a different step for each
group reviewing the content and you'll be able to assign a certain
group of users the ability to take action on it.
This is a pretty complicated Workflow process so it may take a
few minutes to get it working the way you want.
I actually have a similar Workflow that I built that might help
you get started. Give me a minute to post it on our Github
repository for Sample
Workflows. Might be better to place it there long-term rather
than just attaching it to this thread.