First, you should only share files out of the /Users/Shared folder, not from your user's home folder. Nothing particularly wrong, but it is messy due to the permissions set on your home folder.
Second, you likely want a file server which is not the same as file sharing. You can set up your Mac to act as a file server, but it takes some work in the Terminal. File Sharing just lets the others see the files. They cannot edit them without making a copy.
Third, you should create Sharing Only users for the others in the office unless they need an account on your Mac (because they use that Mac). File Sharing on macOS is essentially logging into the Mac remotely. If they have an account on that Mac, they will have the same access they would have if they sat down at the Mac and logged into their account.
1) Start by creating a top-level folder inside /Users/Shared/. Add any files and subfolders you want to share into that folder, too.
3) Create your users in Users & Groups selecting Sharing Only from the popup menu.
Create a Group and add all of the office users to the group (same as creating a user, but select Group from the popup menu).
2) Here is the ACL you need to add to the top-level folder you created inside Shared. You will need to modify it to change <directory_name> and change the <groupName> to whatever you created.
chmod -R +a "group:<groupName> allow list,add_file,search,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity,file_inherit,directory_inherit" "/Users/Shared/<directory_name>/"
Copy it into TextEdit and change those items. Then copy and paste into a Terminal window, hit return.
That access control entry (ACE) gives everyone in the group the ability to edit files and folders created by others in the group. Any folders added will inherit the ACE, thus all subfolders created will get the ACE. The -R tells it to write the ACE to all of the contents of the folder including subfolders.