Add javascript to wp_head with call to plugin options?

Nesting functions in PHP very rarely makes sense. There are some advanced reason for doing it, but I doubt they are needed in this case.

class TweetFeedIt {
    function tweet_feed_it() {
        function twitter_username_callback() {
            function tweet_count_callback() {
                [...]
            }
        }
    }
}

The add_action() function can take up to 4 parameters, but those parameters are not the names of the nested functions you wrote above.

add_action('wp_head', 'tweet_feed_it', 'twitter_username_callback', 'tweet_count_callback');

Read the documentation for PHP, for add_action() and for adding scripts. PHP does exactly what you tell it to do, but you have to follow the conventions of the language.