You don’t have to run through The Loop in one go.
$args = array(
'posts_per_page' => 3,
'category__in' => array(
4,
5,
),
);
$querytest = new WP_Query($args);
if ($querytest->have_posts()) {
// this is the first post, with its markup
$querytest->the_post();
?>
<div class="width-1-2">
<?php get_template_part('content', 'front', get_post_format());
</div>
<div class="width-1-2">
<div class="row">
<?php
// here com the second and third post, wrapped in their additional markup
for ($i = 0; $i < 2; ++$i)
if ($querytest->have_posts()) {
$querytest->the_post();
?>
<div class="width-1-2">
<?php get_template_part('content', 'front', get_post_format());
</div>
<?php
}
?>
</div>
</div>
<?php
} else {
// no posts found
}
I hope this gives you an idea and gets you started customizing this to suit your needs.