<?php
$families = array(
"Griffin" => array(
"Peter",
"Louis",
"Chris",
"Stewie",
"Meg"
));
 
$the_array = 'families';
$answer = 'Peter';
$array_key = 'Griffin';
 
$the_array = ($$the_array);
if (in_array($answer, $the_array[$array_key])) {
    echo "you nailed it";
} else {
    echo "neah";
}

?>