Zkuste použít pro každou smyčku místo while
data[0][firstName] James
data[0][lastName] Smith
data[1][firstName] Jane
data[1][lastName] Doe
data[2][firstName] Bob
data[2][lastName] Builder
etc..
foreach($data as $d){
$person_fname = $d['firstName'];
$person_lname = $d['lastName'];
$query_init2 = "INSERT INTO person ( first_name, last_name) VALUES (:person_fname,:person_lname);";
$query_prep2 = $db_con->prepare($query_init2);
$insert_result2 = $query_prep2->execute(array(
"person_fname" => $person_fname,
"person_lname" => $person_lname
));
}