Complex sentence: Panuh was surprised to see his brother are supporting him for marriage on first night of marriage, they pretended to enjoy and participate in the marriage celebrations and forced Punnun to drink different types of liquor.
Split into simpler sentences: Panuh was surprised to see his brother are supporting him for marriage on first night of marriage. That night (first night of marriage), they pretended to enjoy and participate in the marriage celebrations and forced Punnun to drink different types of liquor.