同一页面上的两个表单和php脚本无法正常工作

there are two forms one is registration form and another is sign in form .When am registring with registration form its div element is fetching message from php using isset funtion but when i am doing same thing with sign in it is redirecting page to homepage please help what can i do if am trying to match database if not matched it will fetch value from php and show in the div as in the code

    <?php 
    if (!empty($_POST['finish'])) {
       //do something here;
    include'php/signup.php';
    }

    if (!empty($_POST['go'])) {
       include'php/signin.php';
    }
    ?>      

    <html>
    <head>        
    <link rel="stylesheet" type="text/css" href="css/homepage.css">
    <link rel="stylesheet" type="text/css" href="css/login.css">
    <link rel="stylesheet" type="text/css" href="css/signup.css">
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
    <script src="js/login.js"></script> 
    <script src="js/signup.js"></script>        
    <script>
    function hideMessage() {
        document.getElementById("message").style.display = "none";
    };
    setTimeout(hideMessage, 5000);
    </script>
    </head>
    <body >
    <!--row starts here -->

    <div class="row">
    <div class="col-1-2">
    </div>
    <div class="col-1-2">
       <div class="container">

      <ul class="tabs">
        <li class="tab-link current" data-tab="tab-1">Sign Up</li>
        <li class="tab-link" data-tab="tab-2">Sign In</li>            
      </ul>        
      <div id="tab-1" class="tab-content current">            
    <div id="message"><?php if(isset($message)) echo $message; ?></div>
    <ul id="registration-step">
    <li id="account" class="highlight">Account</li>
    <li id="password">Password</li>
    <li id="general">Nick Name</li>
    </ul>
    <form name="frmRegistration" id="registration-form" method="post">
    <div id="account-field">
    <span id="email-error" class="registration-error"></span>
    <div><input type="text" name="email" id="email" class="demoInputBox" placeholder="E-mail"/></div>
    </div>        
    <div id="password-field" style="display:none;">
    <span id="password-error" class="registration-error"></span>
    <div><input type="password" name="password" id="user-password" class="demoInputBox" placeholder="Password"required /></div>        
    </div>        
    <div id="general-field" style="display:none;">        
    <div><input type="text" name="nickname" id="display-name" class="demoInputBox" placeholder="Nick Name"/></div>        
    </div>
    <div>
    <input class="btnAction" type="button" name="back" id="back" value="Back" style="display:none;">
    <input class="btnAction" type="button" name="next" id="next" value="Next" >
    <input class="btnAction" type="submit" name="finish" id="finish" value="Finish"  style="display:none;">
    </div>
    </form>        
    </div>     
     <div id="tab-2" class="tab-content">
    <div id="signinmsg"><?php if(isset($msg1)) echo $msg1; ?></div> 
    <form  name="signin"method="post">
        <input type="text" name="signinemail"class="demoInputBox"placeholder="E-mail">
        <br><br>
        <input type="text" class="demoInputBox"name="signinpass"placeholder="Password"><br><br>
    <input class="btnAction" type="submit" name="go" id="go" value="Go.." >     
    </form>
    </div> 
    </div>
    </div>        
    <!--this row ends here -->        
  </body>        
    </html>

You should be checking if isset and not !empty

<?php 
    if (isset($_POST['finish'])) {
       //do something here;
    include'php/signup.php';
    }

    if (isset($_POST['go'])) {
       include'php/signin.php';
    }
?>