dragging overview can't reorder siblings

I'm not entirely sure what you mean.

However, I will try giving some sort of help.

If you have some rows with several columns. (figure #1)

<div id="row-1" class="row">
<div id="col-1-1" class="col-md-4">...</div>
<div id="col-1-2" class="col-md-4">...</div>
<div id="col-1-3" class="col-md-4">...</div>
</div>

<div id="row-2" class="row">
<div id="col-2-1" class="col-md-4">...</div>
<div id="col-2-2" class="col-md-4">...</div>
<div id="col-2-3" class="col-md-4">...</div>
</div>
figure #1

You can drag say the div with id="col-2-2" from row-2 and drop on top of row-1 that div and all it's children will be relocated at the bottom of row-1, it will become the last sibling of row-1. (figure. #2)

<div id="row-1" class="row">
<div id="col-1-1" class="col-md-4">...</div>
<div id="col-1-2" class="col-md-4">...</div>
<div id="col-1-3" class="col-md-4">...</div>
<div id="col-2-2" class="col-md-4">...</div>
</div>

<div id="row-2" class="row">
<div id="col-2-1" class="col-md-4">...</div>
<div id="col-2-3" class="col-md-4">...</div>
</div>
figure #2

You can also drag that same div with id="col-2-2" (if you want) and drop it in between any of the other columns of either row-1/row-2. A thin blue line appears either above or below, depending on if you want to put the div before or after the sibling your trying to drop it near. (figure #3)

<div id="row-1" class="row">
<div id="col-1-1" class="col-md-4">...</div>
<div id="col-2-2" class="col-md-4">...</div>
<div id="col-1-2" class="col-md-4">...</div>
<div id="col-1-3" class="col-md-4">...</div>
</div>

<div id="row-2" class="row">
<div id="col-2-1" class="col-md-4">...</div>
<div id="col-2-3" class="col-md-4">...</div>
</div>
figure #3

Hope that helps

Saj