yes I would do that recursively for the site folders only. But I am going to start as if you just created the group.
So you now have a group called rategrp - edit the /etc/group folder and add the users to that group that will require the write permissions. Then change the group-owner for the three sites. Once you have done that go through the folders and assign the permissions that they need. If you want the whole site writable then just do the following
chgrp -r rategrp /home/<enter site name>
chmod 775 -r /home/<enter site name>
that should allow three users write access to the sites. You will have to do this for the other two sites also.