Login dengan 3 tabel

Permisi, saya sedang membuat proses login menggunakan 3 tabel, ada terjadi beberapa kesalahan , mohon koreksi nya master kesalahan terdiri dari : Notice: Undefined index: nis in C:\xampp\htdocs\RiwaldiXIIRPL2\cek_login.php on line 7

Notice: Undefined index: id_guru in C:\xampp\htdocs\RiwaldiXIIRPL2\cek_login.php on line 9

Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\RiwaldiXIIRPL2\cek_login.php on line 13

Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in C:\xampp\htdocs\RiwaldiXIIRPL2\cek_login.php on line 21

Bagaimana solusinya , sebelumnya terimakasih ^^

<?php
session_start();
include 'koneksi.php';

$username = $_POST['username'];
$password = $_POST['password'];
$us1 = $_POST['nis'];
$pw1 = $_POST['password'];
$us2 = $_POST['id_guru'];
$pw2 = $_POST['password'];

$data = mysqli_query($koneksi,"select * from admin where username='$username' and password='$password'");
$array = mysqli_fetch_array ($data);

$data1 = mysqli_query($koneksi,"select * from siswa where nis='$us1' and password='$pw1'");
$array1 = mysqli_fetch_array ($data1);

$data2 = mysqli_query($koneksi,"select * from guru where id_guru='$us2' and password='$pw2'");
$array2 = mysqli_fetch_array ($data2);

if (mysqli_num_rows($data) == 1) {
    $_SESSION['username'] = $array['username'];
    $_SESSION['password'] = $array['password'];
    $_SESSION['status'] = 'login';
    header ('location:admin/home.php');
}
 else if (mysqli_num_rows($data1) == 1) {
    $_SESSION['nis'] = $array1['nis'];
    $_SESSION['password'] = $array['password'];
    $_SESSION['status'] = 'login';
    header ('location:siswa/home.php');
}
else if (mysqli_num_rows($data2) == 1) {
    $_SESSION['id_guru'] = $array2['id_guru'];
    $_SESSION['password'] = $array['password'];
    $_SESSION['status'] = 'login';
    header ('location:admin/home.php');
}

?>