This is the perfect use case of display:contents;
(https://caniuse.com/#feat=css-display-contents)
display: contents
causes an element’s children to appear as if they were direct children of the element’s parent, ignoring the element itself. This can be useful when a wrapper element should be ignored when using CSS grid or similar layout techniques.
.container {
display:flex;
}
.one {
display:contents;
}
.one p:first-child {
order:2;
}
<div class="container">
<div class="one">
<p>Content 1</p>
<p>Content 3</p>
</div>
<p>Content 2</p>
</div>