What is the ruling on accepting a gift on the occasion of Christmas, and is it permissible to eat sweets made for this occasion, or to accept a gift bought for it, even if it is presented on another day?

Celebrating birthdays is an innovation (bid'ah) and an imitation of the disbelievers (kuffar), and it is forbidden to celebrate them. You should advise your family that it is an impermissible matter, and not to participate in it, and to avoid anything that suggests approval of it. Do not accept gifts given for this occasion. If you fear damaging the relationship, then explain that your acceptance of the gift is for the sake of friendship, not for the innovation, while making it clear to them that you will not accept such gifts in the future and will not give gifts on their birthdays. Avoid eating food and sweets specifically prepared for this occasion.