Some help with its implementation?
Install the Wire library if you have not already got it and look at the examples
See also Wire - Arduino Reference for examples and explanations. The Master Writer/Slave Reader example would make a good place to start.
Will i have to upload a code to each tool Arduino so they can run a G-Code .txt file?
Getting the data to the Arduino is just the first step. Each Arduino will need to be running a program that interprets the G-Code and outputs the appropriate commands to its spindle to move it X, Y, Z and control its speed.