What is the ruling on saying "denounce the religion of his parents" with the intention of harming the other party, and does that necessitate uttering the Two Testimonies for fear of disbelief?

Such a phrase is repugnant and should be avoided, but it is not considered an explicit insult to the religion of Islam. Therefore, its utterer is not judged to be an apostate unless he explicitly states an intention to insult the religion. The default is that a Muslim remains a Muslim, and he is not expelled from Islam except with certainty. A Muslim is not excommunicated for ambiguous words or actions. It is preferable to keep a Muslim within Islam if there is any single reason to do so, acting upon the hadith: "Ward off the prescribed punishments from Muslims as much as you can." It should also be noted that the fiancée is a stranger to the suitor until the marriage contract is concluded, and it is not permissible to speak with her except out of necessity and without a submissive tone of voice.