Question on Share Setup. (Is this possible?)

[steve at 1mercury.net]

I want to set up a Samba share (ShareX) on my Linux
Fileserver.  

GroupA will have read/write access to ShareX.

Users Sam, Jane, Jill will not belong to GroupA but will
also be able to read/write to ShareX.  

GroupA will be able to access all files in ShareX. 

Sam, Jane, Jill will only be able to access their own files
within ShareX.

Is it possible to do this?  If so, what would the share
definition(s) look like in smb.conf? 

If anyone can help me on this one I would be most
appreciative.  

-Steve Maier
steve at 1mercury.net