新婚快乐 is the standard wedding congratulation phrase, equivalent to 'Congratulations on your marriage!' 新婚夫妇 or 新婚夫妻 means newlywed couple.
culture
At Chinese weddings, red 红包 (red envelopes with money) are given to the newlyweds. Common amounts are even numbers, with 6, 8, and 9 being especially auspicious.
