how do I force group mode in homes shares

[ricksaul59]

I wish to force the group to write to a home folder but only with the group of the owner, as other users who have access to the home folder write with their group name. Then no-one else can access the file. I know I can do this with setting the group id (chmod g+s foldername) but I want to do this globally in the samba share.. I have tried force group = %g and other options but nothing seems to work, Any ideas welcome.