How to add only the theme font choices and remove the Google fonts from Beaver Builder. See the image in the comment.

remove-google-fonts-add-default-fonts-beaver-builder.php

<?php
//don't add again

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add_action( 'wp_head', 'childprefix_beaver_builder_modifications', 0 );
/* 
 * Beaver Builder Builder Enabled Modifications
 * Apply childprefix_replace_system_fonts_with_theme_fonts();
 * Apply childprefix_remove_google_font_optgroup_beaver_builder_interface();
 */
function childprefix_beaver_builder_modifications() {

	if ( ! class_exists( 'FLBuilder' ) && ! FLBuilderModel::is_builder_enabled() ) return;

	add_action( 'wp_head', 'childprefix_remove_google_font_optgroup_beaver_builder_interface' );
	add_filter( 'fl_builder_font_families_system', 'childprefix_replace_system_fonts_with_theme_fonts', 10, 3 );

}

/* 
 * Remove Google Fonts from Beaver Builder via CSS only
 */
function childprefix_remove_google_font_optgroup_beaver_builder_interface() {
	echo '<style>optgroup[label=\'Google\'] {display: none!important;}</style>';
}

/* 
 * Replace Beaver Builder System Fonts with Choices from Theme
 * Ref: http://kb.wpbeaverbuilder.com/article/234-add-web-fonts-to-your-theme-and-page-builder
 */
function childprefix_replace_system_fonts_with_theme_fonts() {

	$body[ 'Unna' ] = array(
        'fallback' => 'sans-serif',
        'weights' => array(
            '400',
            '700'
        ),        
    );
	
	$script[ 'Kaushan Script' ] = array(
        'fallback' => 'sans-serif',
        'weights' => array(
            '400',
        ),        
    );
	
	return array_merge( $body, $script );
	
}