Unlicensed Users can access any SharePoint Sites based on whatever permission they have. If you add the unlicensed user to site owner group, the unlicensed user can create a site.
If the Users are inside your organization and need access only to SharePoint Sites they do not require any Office365 Licenses at least for now. You just need their Office365 ID created either by Sync or Manually, whatever method you follow for regular users. The Only difference is you create account without assigning any License to it.