Peace,
Dont assume its a sin because you heard others say it is, what do you feel about it? Its about our intentions and in the end only God knows and will judge us on them. I was born and raised as a Roman catholic for 35 years, and then I became a Quran/ God alone Muslim for the last six years. My wife and my entire family are all still practicing catholics, and most of them didnt accept that I converted to Islam, in fact a few of my brothers told me im crazy and losing my mind, but I never gave up on my beliefs. So, as to celebrating their holidays I dont see the harm in it, as long as you dont openly say your worshipping Jesus or mary or any other saints etc, it should be ok. I usually try to use these occasions to subtley question their beliefs and make them think about what they really beleive, and it has worked some, yet I still show them respect for their beliefs and celebrations. We just had christmas and I bought everyone gifts, and they appreciate that I do this even though im Muslim now, so I am slowly winjing their admiration and respect. I think they assumed i was going to be like the muslims they see on tv with big beards and screaaming Allahu Akbar at them while calling them infidels or something. I even made my wife a wooden shelf in the shape of a crucifix (kinda invented that design) and gave it to her for valentines day recently. She realy loved it and it has made her start to accept me as a Muslim a little more I think, she sees that im open and respectful and even supporting her in her beliefs and it is making her more curious about what exactly a Muslim is and believes. I also let her raise our children in the catholic church since I do think they still teach alot of things that are very admirable and good, and I beleive that it is still important for them to have a strong religious foundation to grow and build upon. I am hoping as they get older and begin to think and question more on their own I will start to let them know what I beleive and why, I dont think it will be too big of a leap for them to accept God alone and to let go of the version of jesus they have been taught. Finally, though i still go to church with them now and then, I do not participate in the mass where they eat and drink the bread and blood of jesus, though I get alot of stares at people curious why I dont go up and just sit in my seat by myself, especially as they all know me here as I grew up in the church with most of them, I think it is earning my families respect . So be accepting, open, and supportive, just dont cross the line you have in your conscience as to what you beleive is acceptable to God or not.
Kurt