Adding users and giving special permissions

I have tried different things with chmod and adduser commands but it will take too much time for me to do this.
Here is what I try to do:
Lets say I will add 3 users to my system. Each user can read the files in the home directories of others but cannot write in it cannot change them. Each user can only write to their own home directory. Also there will be one common directory that everyone can write and read.
I have a lot of users. I don't want to add each one by one.
Thanks a lot for helping :)