Changes values form php

I created a profile page and a edit page, to edit the value of the profile page, like his name, surname, mail or even the password.

I have 2 issues, - one is that even if there is nothing in 'Nom' and 'Prénom' it still changes and then I have an empty string at the place of the inputs - and the second one is that it don't change the mail and password, no error are thrown but nothing change thank you for your help

<?php
if(!isset($_SESSION)){
    session_start();
}

$bdd = new PDO('mysql:host=localhost;dbname=espace_membres', 'root', '');

//pour afficher les données
if(isset($_SESSION['id']))
{

    $requser = $bdd->prepare("SELECT * FROM membres WHERE id = ?");
    $requser->execute(array($_SESSION['id']));
    $user = $requser->fetch();

//une fois qu'il clique sur bouton confirmer
if(isset($_POST['formParamProfil']))
{
        $pwdconnect = sha1($_POST['pwdconnect']);
        $requser = $bdd->prepare('SELECT * FROM membres WHERE motdepasse = ?');
        $requser->execute(array($pwdconnect));
        $userexist = $requser->rowCount();
        if($userexist == 1)
        {

                if(isset($_POST['newnom']) AND !empty($_POST['newnom']) != $user['nom'])
                {
                    $newnom = htmlspecialchars($_POST['newnom']);
                    $insertnom = $bdd->prepare("UPDATE membres SET nom = ? WHERE id = ?");
                    $insertnom->execute(array($newnom, $_SESSION['id']));
                    //header('Location: profil.php?id='.$_SESSION['id']);
                } else {
                    $erreur = "nom erreur";
                }

                if(isset($_POST['newprenom']) AND !empty($_POST['newprenom']) != $user['prenom'])
                {
                    $newprenom = htmlspecialchars($_POST['newprenom']);
                    $insertprenom = $bdd->prepare("UPDATE membres SET prenom = ? WHERE id = ?");
                    $insertprenom->execute(array($newprenom, $_SESSION['id']));
                    //header('Location: profil.php?id='.$_SESSION['id']);
                } else {
                    $erreur = "prénom erreur";
                }

                if(isset($_POST['newmail']) AND !empty($_POST['newmail']) AND isset($_POST['newmail2']) AND !empty($_POST['newmail2']) != $user['mail'])
                {
                    if(filter_var($mail, FILTER_VALIDATE_EMAIL)) {
                        $reqmail = $bdd->prepare("SELECT * FROM membres WHERE mail = ?");
                        $reqmail->execute(array($mail));
                        $mailexist = $reqmail->rowCount();
                        if($mailexist == 0) 
                        {
                            $newmail = htmlspecialchars($_POST['newmail']);
                            $insertmail = $bdd->prepare("UPDATE membres SET mail = ? WHERE id = ?");
                            $insertmail->execute(array($newmail, $_SESSION['id']));
                            //header('Location: profil.php?id='.$_SESSION['id']);
                        }
                    } else {
                        $erreur = "L'adresse mail existe déjà";
                    }
                }

                if(isset($_POST['newmdp']) AND !empty($_POST['newmdp'] AND isset($_POST['newmdp2']) AND !empty($_POST['newmdp2'])) != $user['motdepasse'])
                {

                    $mdp = sha1($_POST['newmdp']);
                    $mdp2 = sha1($_POST['newmdp2']);

                    if ($mdp == $mdp2) {
                        $insertmdp = $bdd->prepare("UPDATE membres SET motdepasse = ? WHERE id = ?");
                        $insertmdp->execute(array($newmdp, $_SESSION['id']));
                        header('Location: profil.php?id='.$_SESSION['id']);
                    } else {
                        $erreur = "Vos mots de passes ne correspondent pas";
                    }

                }

                if(isset($_FILES['avatar']) AND !empty($_FILES['avatar']['name']))
                {
                    $tailleMax = 2097152;
                    $extensionsValide = array('jpg', 'jpeg', 'gif', 'png');
                    if($_FILES['avatar']['size'] <= $tailleMax) {
                        $extensionUpload = strtolower(substr(strrchr($_FILES['avatar']['name'], '.'), 1));
                        if(in_array($extensionUpload, $extensionsValide)) {
                            $chemin = "membres/avatars/".$_SESSION['id'].".".$extensionUpload;
                            $deplacement = move_uploaded_file($_FILES['avatar']['tmp_name'], $chemin);
                            if($resultat){
                                $updateavatar = $bdd->prepare("UPDATE membres SET avatar = :avatar WHERE id = :id");
                                $updateavatar->execute(array(
                                    'avatar' => $_SESSION['id'].".".$extensionUpload,
                                    'id' => $_SESSION['id']
                                ));

                                header('Location: profil.php?id='.$_SESSION['id']);
                            } else {
                                $erreur = "Il y a eu une erreur lors de l'importation de votre photo de profil";
                            }
                        } else {
                            $erreur = "Votre photo de profil doit être aux formats suivants: jpg, jpeg, gif ou png";
                        }

                    } else {
                        $erreur = "Votre photo de profil ne peut dépasser 2Mo";
                    }
                }


        } else {
            $erreur = "Mot de passe actuel non valide";
        }
}

?>