Have you tested it to confirm that if you select yes for any of them you are taken to the thank_you2.php page?
If so then you only need to add in the else statement for the redirect page. At the end of your custom set session value code you have this:
$_SESSION["inform"] = "thank_you2.php";
}
You should update this to be like this:
$_SESSION["inform"] = "thank_you2.php";
} else {
$_SESSION["inform"] = "<the other page>.php";
}
This will ensure that if the first page is not set to the redirect it will be set to this page specified in the else.