<div class="myAwesomeButtons">
     <button id="first_button" class="blue_button inset_button" style="">First</button>
     <button id="second_button" class="green_button inset_button" style="display: none;">Second</button>
     <button id="third_button" class="other_button">Third</button>
</div>

function fixButtons() {
    document.getElementsByClassName("myAwesomeButtons")[0].style.visibility='hidden';
    document.getElementsByClassName("myAwesomeButtons")[1].style.visibility='visible';
}

fixButtons();

function fixButtons() {
  var buttonGroup = document.getElementsByClassName("myAwesomeButtons")[0].getElementsByTagName("button");
  buttonGroup[0].style.visibility='hidden';
  buttonGroup[1].style.visibility='visible';
}

function fixButtons() {
    var button1 = document.getElementById("first_button");
    button1.style.display= "none";
    var button2 = document.getElementById("second_button");
    button2.style.display= "inline";
}