JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <tr>
        <td id="tabela">
            <input type="text" id="tabelainput" class="janmembros" maxlength="3" name="janmembros" value="1" disabled>
        </td>
        <td id="tabela">
            <input type="text" id="tabelainput" class="janvisitantes" maxlength="3" name="janvisitantes" value="3" disabled>
        </td>
        <td id="tabela3" class="jantotal">
        </td>
    </tr>
</table>
        
<table>
    <tr>
        <td id="tabela">
            <input type="text" id="tabelainput" class="janmembros" maxlength="3" name="janmembros" value="1" disabled>
        </td>
        <td id="tabela">
            <input type="text" id="tabelainput" class="janvisitantes" maxlength="3" name="janvisitantes" value="2" disabled>
        </td>
        <td id="tabela3" class="jantotal">
        </td>
    </tr>
</table>
        
<table>
    <tr>
        <td id="tabela">
            <input type="text" id="tabelainput" class="janmembros" maxlength="3" name="janmembros" value="1" disabled>
        </td>
        <td id="tabela">
            <input type="text" id="tabelainput" class="janvisitantes" maxlength="3" name="janvisitantes" value="5" disabled>
        </td>
        <td id="tabela3" class="jantotal">
        </td>
    </tr>
</table>
        
<table>
    <tr>
        <td id="tabela">
        </td>
        <td id="tabela">
        </td>
        <td id="tabela3" class="total">
        </td>
    </tr>
</table>

JavaScript

if ( $( ".janmembros" ).val() != '' && $( ".janvisitantes" ).val() != '' )
{
    $('table').each(function() {
        var $this = $(this),
            janmembros = parseInt($this.find( ".janmembros" ).val()),
            janvisitantes = parseInt($this.find( ".janvisitantes" ).val());
    
        $this.find( ".jantotal" ).html( janmembros+janvisitantes );
        $( ".total" ).html($this.find( ".jantotal" ).html());
    });
    
}