Arduino keypad matrix example? ( teensyduino )
By your description, you don't have a matrix.  You have them wired as just 8 straight switches.

A matrix would be if you had the 4 switch pins of one keypad wired to the same switch pins of the other keypad, and the two common connections from the keypads wired to two separate IO pins.

At the moment your code is responding whenever a button is in the low state. Instead it needs to respond only when the button transitions from the high state to the low state.  To do that you need to know what state all the buttons were in the previous pass through loop to compare them to what they are in this pass through loop - and if any have changed then they have either been pressed or released.

You should also implement debouncing to that you don't get false presses.

If you don't want to learn how to do all that yourself I have a handy library that will do it all for you:


https://github.com/MajenkoLibraries/DebouncedInput


If you want to convert your setup to an actual matrix to save on IO pins you want to read the Arduino Keypad tutorial:


http://playground.arduino.cc/Main/KeypadTutorial