JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.2.2/jquery.min.js"></script>
<select class="quantity" id="one" name="double room">
    <option value="1" selected>1</option>
    <option value="2">2</option>
    <option value="3">3</option>
</select>


<select class="quantity" id="two" name="double room">
    <option value="2" selected>2</option>
    <option value="3">3</option>
</select>

JavaScript

// Intialize this value with the option missing from #two
var previousValue = 1;

// Do stuff on change.
$('#one').on('change', function() {

    // Put the unselected option from #one back in #two.
    $('#two').append('<option value="' + previousValue + '">' + previousValue + '</option>');
    
    // Remember what we had.
	previousValue = $('#one').val();
    
    // Remove the option from #two selected in #one.
	$('#two').children('[value="' + $('#one').val() + '"]').remove();
    
})