Root logins are generally considered to be a major no-no, for the very reason you state in your post. It is time consuming and sometimes difficult to determine who logged in as "root" at a given time, especially when 20 or more people have root access to your boxes. You may be able to sort it out but its not going to be fun.

The simple way to solve your main problem is to disallow root logins and force users to use su or sudo. Assuming they all need root access (doubtful but possible). When root access is needed for more than one command su leaves a message in the system log stating the user who su'd and the terminal they did it from.