The user field will return an array of arrays.
$users = get_field('guests2');
// for testing
echo '<pre>'; print_r($users); echo '</pre>';
if ($users) {
foreach ($users as $user) {
$userID = $user['ID'];
$profile_image = get_field('profile_image', 'user_'. $userID);
$biography = get_field('biography', 'user_'. $userID);
// code for displaying values here
}
}