How can two non-Muslim women who are about to get married, and who have been in forbidden relationships with their fiancés, be guided and reminded with flexible and appropriate phrases without offering them congratulations?

It is permissible to congratulate non-Muslims on their personal non-religious occasions with phrases that do not justify previous forbidden relationships and do not indicate approval of their religion, such as "Happy marriage" or "May Allah make you happy." The congratulation can also include an invitation for them to be content with marriage instead of previous forbidden relationships, or an invitation to Islam.