SubhanAllah, SubhanAllah. brothers and sisters in islam we are NOT ALLOWED TO SAY MERRY CHRISTMAS and the MAJORITY of scholars agree. As muslims we can only say eid mubarak or happy eid to each other on OUR FESTIVALS. by saying Merry christmas you agree with what they're doing which is wrong. here's a fatwa. so do not do something outside of the sunnah for the sake of respecting a non muslim or in any case a human being. Allah is more deserving of your respect and gratitude than the Kuffar. subhanAllah. Do not justify this matter. you can tell them and explain to them of what your beliefs are against saying merry christmas. Whatever Allah swt and his messenger say we must FOLLOW. please read the fatwa below.
It is not permissible to congratulate the kuffaar on their festivals in any way whatsoever
What is the ruling on eating the food (rice, meat, chicken or cake) that is given to us by a Christian friend that he made for his birthday or for Christmas or the Christian New Year? What is your opinion on congratulating him by saying, “Insha Allaah you will continue to do well this year” so as to avoid saying Kull ‘aam wa antum bi khayr (approx. “season’s greetings”) or “Happy New Year” etc?.
Praise be to Allaah.
It is not permissible for a Muslim to eat things that the Jews and Christians make on their festivals, or what they give him as a gift on their festivals, because that is cooperating with them and joining in with them in this evil, as is explained in question no. 12666.
It is not permissible for him to congratulate them on their festivals in any way whatsoever, because that implies approval of their festival and not denouncing them, and helping them to manifest their symbols and propagate their innovation, and sharing their happiness during their festivals, which are innovated festivals that are connected to false beliefs that are not approved of in Islam. See also question no. 47322.
And Allaah knows best.
Islam Q&A