Wa `alaykum as-salam waramatullah wabarakatuh!
Dear sister, thanks for your question. First of all, I need to welcome you to the fold of Islam. May Allah the Almighty help you get accustomed to this new life and abide by the rules of this religion, revealed to guide mankind.
Islam, dear Sister, does not demand that Muslims live in social isolation; rather it urges us to be interactive and proactive. Islam requires of every Muslim to be a good example and a means for Islam's light to reach others. That’s why we see that as it stretches its arm to embrace every newcomer, welcoming him/her to its fold, Islam covers that person with its radiating light. But it does not cut off his/her relations with others, i.e with those who have not yet made up their mind or those who prefer to stay out of the Islamic fold. Rather, part of what makes one a true Muslim is to strive hard for the message of Allah to reach all people. But this should be done through good manners, wisdom and an approach using logic.
Before going further into this topic, I want to mention Islamic teachings about human relations. In addition to regulating how Muslims conduct affairs and relations with his fellow Muslims, Islam guides Muslims towards noble dealings and good conduct with people in general, without any kind of discrimination due to differences in faith or race.
A key part of this is the Muslim’s relation with his non-Muslim family, relatives, friends, neighbors etc.,. He should deal with them on the basis of justice and righteousness. Your conversion to Islam does not cut your family bonds, especially to your parents. Even if they happen to be non-Muslims, you still owe them rights of obedience and dutifulness. You must still care for them and pray for their guidance. You never know, perhaps Allah will make you the cause of their embracing Islam.
Thus, in the light of these teachings, renowned Muslim scholars have made it clear that being a Muslim does not mean that a person has nothing to do with his/her non-Muslim family or relatives, even if they turn hostile to him because of his conversion to Islam. We need to strengthen our relations with all people for through this we will be able to reach out to them, conveying Allah’s message and trying to make them understand Islam. This is based on the following Qur’anic verse:
So this means that Muslims are allowed to share with non-Muslim their joyous occasions, wishing them happy holidays. You may even send greeting cards to your Christian friends, relatives or neighbors. If they give you gifts, you should thank them and accept them with good cheer and should also remember them at the times of Islamic holidays. Therefore, there is nothing in Islam that prevents you from being with your family during Christmas, at least to show them that you are part and parcel of them even after your conversion to Islam.
God forbids you not, with regard to those who fight you not for (your) Faith nor drive you out of your homes, from dealing kindly and justly with them: for God loveth those who are just.
Surah 60 Verse 8
You said that your family is partially religious, in the sense that they strongly believe in God. This means that they are likely to get attracted towards Islam. But maybe the only person that can do so is you, through the wise and calm methods you adopt in presenting your ideas.
However, I need to make it clear to you that you are not allowed to go beyond sharing your family’s joyous mood of the feast, for you are not allowed to celebrate Christmas with them. You have to make them understand that your presence with them means a lot to you, yet you cannot return to old habits, like drinking and dancing. They should know you expect them to respect that. Try to draw them to awareness that since you have chosen Islam as a way of life you must not do anything that contradicts the principles of your religion. You should be clear with your family that your attendance is in order to be with the family, that your belief in Jesus is firmly according to Islamic teachings and that, were it not for being with the family, you would not be doing anything special to mark Christmas day.
Sister, you are to know that as we deal with people, interact with them socially, we must never forget that we have our own unique identity. This identity means that we have announced our commitment to follow Allah’s way and abide by His rules. Part of which, is not to mix anything alien to His Religion.
So from this, scholars have deduced a juristic ruling that Muslims must not celebrate festivals or holidays that are for non-Muslims. They emphasize that Islam suffices Muslims. So there is no need for us to imitate others; our religion is comprehensive in itself and it embraces all that is good. So Muslims are supposed to be the model for others, not vice versa. This is based on the hadith of the Prophet (pbuh) in which he says:
‘He who imitates others is reckoned as one of them.’ (Abou Dawoud)
Your family may find this odd in the beginning, especially as it will be the first Christmas they will celebrate without you actively participating. But as time goes on, I’m sure they will understand. Your presence with them will also be valued in addition to sending them greeting cards and exchanging gifts with them. But you must make sure that the gifts you send do not amount to something haram in your religion, like wine, etc. Showing compliments and felicitation here, must not collide with the principles of your religion.
Islam tends to build a strong personality that would never sway by any circumstances. This point is very clear and renowned Muslim scholars are unanimous on it. For instance, read what Sheikh Yusuf Al-Qaradawi says here:
"This sheds light on mutual rights (between Muslims and non-Muslims). If a friend of yours from among the People of the Book tends to share your joyous occasions during your feasts and `Iids and never fails to share your grief at times of calamities, then there is nothing wrong in you showing him the same feelings in return, for Allah Almighty says:
But this does not mean that we should celebrate with them. What we are required to show, is part of righteousness and justice well established in Islam.”
When a (courteous) greeting is offered you, meet it with a greeting still more courteous, or (at least) of equal courtesy. God takes careful account of all things.
Surah 4 Verse 86
So sister, you see. Islam does not erect a wall separating you from your family. Rather, it lays strong emphasis on keeping good relations with them. This is especially with your parents, whom you owe dutifulness and obedience, as long as that does not involve disobedience to the Great Creator, Almighty Allah.
Actually, parents have a very special position that is stated in the Qur’an:
I hope this clarifies matters, sister.
And We have enjoined on man (to be good) to his parents: in travail upon travail did his mother bear him, and in years twain was his weaning: (hear the command), "Show gratitude to Me and to thy parents: to Me is (thy final) Goal.
"But if they strive to make thee join in worship with Me things of which thou hast no knowledge, obey them not; yet bear them company in this life with justice (and consideration), and follow the way of those who turn to me (in love): in the end the return of you all is to Me, and I will tell you the truth (and meaning) of all that ye did."
Surah 31 Verses 14 – 15
Wishing you all the best, thanks and please keep in touch.