create a shared group
Code:
sudo groupadd sharedfolder
then add the list of users to the group
Code:
echo 'user1|user2|etc|...' | while IFS=\| read -r u; do sudo usermod -a -G sharedfolder "$u"; done
then change the group and permissions of the folder
Code:
sudo chown -R user:sharedfolder /path/to/folder
find /path/to/folder | while read -r f; do if [ -f "$f" ]; then sudo chmod 0640 "$f"; else sudo chmod 0750 "$f"; fi; done