It depends on how you are going to use the shared directory.
The classic Linux way of doing this sort of thing goes something like this:
 Create the shared folder:
 Create the new user's group:
sudo mkdir /home/Shared
 Change ownership of the shared folder to the new group:
sudo groupadd newgroup
 Add your desired users to that group:
sudo chown :newgroup /home/Shared
Now you have some decisions to make about what you want those users to be able to do:
sudo gpasswd -a morbius newgroup
[a] All group users can add to and delete from the folder and can read and but not write to each others files:
[b] Same as above but only the owner of the file can delete it:
sudo chmod 0770 /home/Shared
[c] All group users can add to and delete from the folder and can read and write to each other's files:
sudo chmod 1770 /home/Shared
[d] Same as [c] except only the owner of the file can delete it:
sudo chmod 2770 /home/Shared
A "1" in the first position of the chmod command is the "sticky bit" which prevents deletion of a file to anyone other than the owner.
sudo chmod 3770 /home/Shared
A "2" in the first position of the chmod command is the "setgid bit" which forces all new or copied files to have the group of that folder.
A "3" in the first position of the chmod command is the combination of the sticky (1) & setgid (+2) bits.
*** There is one caveat to all this as far as the setgid bit is concerned. All new files created in and any files copied to that folder will in fact inherit the group of the folder. But not files moved to that folder. Moved files retain the ownership from wherever they were moved from. One way to get past this problem is to use bindfs.
*** And in turn one caveat to bindfs is that it has no concept of a "sticky bit".