ClearOS does not support this natively. I'm sure I've seen something from Dave about setting up ACL's with Windows style permissions, but I could not find it when I last looked. By going a bit outside ClearOS and flexshares I have a parent share called Shared which my wife and I can access. In it there is also a subfolder, Shared\family which the the broader family can access using a different share name. My wife and I can access the family folder directly through our share, but the broader family cannot access our Shared folder. This required a manual configuration of Samba, but it is very close to the Flexshare set up.