which IP address coects to my server

For some inteal reasons, several people in our company are sharing the same USERNAME when coecting to SERVER, but they coect from different clients and machines.

We need to track what each IP address does on the server.

Can you suggest how to store the time history of the commands organized by IP address, and not by USERNAME (which would be much easier)? Is that even possible?

Specifics: SERVER has Ubuntu 14.04.4 LTS installed, and people are coecting and doing operations on it from both Windows and Linux machines.