Does a Muslim apostatize by mocking committed Muslims or by jokingly saying that he would have returned the greetings of disbelievers on their holidays had they not been present, and does he need to renew his Islam and marriage contract?

What you said about the committed individuals, and your intention to refuse the aforementioned congratulations, does not constitute disbelief (kufr). Apostasy (riddah) does not occur merely by that. It is obligatory for a Muslim to fear Allah alone and to speak nothing but the truth. None of what was mentioned is binding upon you. Abandon these whispers (waswas).