Dude I made a simple example it does not use CSS just what is BS4 default. The idea is the same one that you have already used, but it has 2 logos, one that only appears in Mobile in the middle of the bar and the icons on the left that only appear in mobile tb.
OBS 1: Navbar by default already has display:flex
, and justify-content: space-between
so there are 3 items one will always be left, another to the center and the last to the right.
OBS 2: You do not need float
classes to align
See how it was in the example below, and have tb displayed in "All Page" to see how it goes in Desktop vs. Mobile version
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>Page Title</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" type="text/css" media="screen" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" />
<link rel="stylesheet" type="text/css" media="screen" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css" />
<style>
</style>
</head>
<body>
<nav class="navbar navbar-expand-lg navbar-dark bg-info">
<a href="/" class="navbar-brand d-none d-lg-block">Brand</a>
<div class="d-block d-lg-none">
<ul class="nav d-flex ">
<li class="nav-item"><a class="nav-link text-white" href=""><i class="fa fa-twitter"></i></a></li>
<li class="nav-item"><a class="nav-link text-white" href=""><i class="fa fa-github"></i></a></li>
</ul>
</div>
<a href="/" class="navbar-brand d-block d-lg-none">Brand</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbar4">
<span class="navbar-toggler-icon"></span>
</button>
<div class="navbar-collapse collapse" id="navbar4">
<ul class="navbar-nav">
<li class="nav-item active">
<a class="nav-link" href="#">Link <span class="sr-only">Home</span></a>
</li>
<li class="nav-item">
<a class="nav-link" href="//codeply.com">Codeply</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Link</a>
</li>
</ul>
</div>
</nav>
<script src="https://code.jquery.com/jquery-3.2.1.min.js"></script><scriptsrc="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script><scriptsrc="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.3/js/bootstrap.bundle.min.js"></script>
</body>
</html>