To make something animate, you will need a property that can be manipulated, for example, "left" or "margin-left". You can animate inline or inline-block elements without positioning.
Try relative positioning instead. Set the parent container element (add one if you don't already have):
position: relative;
Set all child elements:
position: absolute;
top: 0;
left: 0px; // 200px, 400px, etc. respectively
Then do a fadeOut or hide on the elements:
$('#selector-for-box-1-and-2')
.fadeOut('slow', function() {
})
Then add in the animation in the animation complete function:
$('#selector-for-box-1-and-2')
.fadeOut('slow', function() {
$('#selector-for-box-3').animate({
left: 0px
}, 1000);
})
You can also apply jQuery.masonry plugin, the animation will be handled automatically when you remove any elements.