WordPress Twitter card info (assumes you've already got basic open graph data via a plugin), tutorial here: http://zoerooney.com/blog/tutorials/increase-share-ability-using-twitter-cards/

wordpress-twitter-cards.php

<?php // Include Twitter IDs for content creator (you, usually) ?>
<meta name="twitter:site" content="@zoe_rooney"/>
<meta name="twitter:creator" content="@zoe_rooney"/>

<?php
// get current post ID 
$currentpost = get_the_ID();

// get radio value
$radio = get_field( 'twitter_card_options', $currentpost );

// assign card type to variable based on radio selection
if ( $radio  == "Use gallery card type" ) :
	$cardtype = 'gallery';

elseif ( $radio  == "Use photo card type" ) :
	$cardtype = 'photo';

else : 
	// default to summary large image
	$cardtype = 'summary_large_image';
endif;
?>

<?php //  meta field for card type with variable in place ?>
<meta name="twitter:card" content="<?php echo $cardtype; ?>"/>

<?php 
// add four specific images if using gallery card using image fields
if ( $radio  == "Use gallery card type" ) : 
	// set a bunch of variables for our image data
	// I'm using thumbnails to keep the file size down
	// thumbnail size must be larger than 160px square
	$image0 = get_field( 'gallery_card_image_1', $currentpost );
	$image0_url = wp_get_attachment_image_src( $image0, 'thumbnail' );
	$image1 = get_field( 'gallery_card_image_2', $currentpost );
	$image1_url = wp_get_attachment_image_src( $image1, 'thumbnail' );
	$image2 = get_field( 'gallery_card_image_3', $currentpost );
	$image2_url = wp_get_attachment_image_src( $image2, 'thumbnail' );
	$image3 = get_field( 'gallery_card_image_4', $currentpost );
	$image3_url = wp_get_attachment_image_src( $image3, 'thumbnail' );
?>
	<meta name="twitter:image0" content="<?php echo $image0_url[0]; ?>"/>
	<meta name="twitter:image1" content="<?php echo $image1_url[0]; ?>"/>
	<meta name="twitter:image2" content="<?php echo $image2_url[0]; ?>"/>
	<meta name="twitter:image3" content="<?php echo $image3_url[0]; ?>"/>
<?php endif; ?>

<?php 
// bonus: gallery image code if you're using the ACF gallery field type
if ( $radio  == "Use gallery card type" ) : 
	// Get gallery field data
	$twitterimages = get_field( 'twitter_card_gallery', $currentpost );
		// set a counter to start at 0 and loop through the images in the gallery
		$index = 0; 
		foreach ( $twitterimages as $image ) : ?>
			// display the meta elements with the correct index number and image URLs
			<meta name="twitter:image<?php echo $index; ?>" content="<?php echo $image['sizes']['thumbnail']; ?>"/>
		<?php $index++; // advance counter
		endforeach; // end loop
endif; ?>