In order to achieve responsiveness with bootstrap you will have to add the classes for all layouts col-**-number
, like col-md-12
, col-sm-12
, col-xs-12
etc.. You can read more about the boostrap grid sytstem and its behaviour. As it concerns the vertical alignment of the divs, its a tricky problem in general depending on the conditions of your divs. Placement, fixed height etc.. There is an excellent guide in CssTricks tackling this exact problem of equal columns you are looking for. As I stated is not trivial.
<div class="container">
<div class="row">
<div class="col-md-8 col-sm-8 col-xs-12">
<img src="http://placehold.it/1280x700" class="imgFullSize">
</div>
<div class="col-md-4 col-sm-4 col-xs-12">
<div class="row">
<div class="col-md-12 col-sm-12 col-xs-12">
<img src="http://placehold.it/452x250" class="imgFullSize">
</div>
<div class="col-md-12 col-sm-12 col-xs-12" style="margin-top: 30px">
<img src="http://placehold.it/452x250" class="imgFullSize">
</div>
</div>
</div>
</div>
</div>