Celebrations and Customs

Muslim business using adverts with Christmas decorations and selling Christmas items

Q: 

1. Is it permissible for a Muslim business owner to promote his business using adverts with Christmas decorations? 

2. Can a Muslim businessman sell Christmas lights, trees, decorations, etc.? 

3. What is the ruling regarding a person decorating his business with Christmas lights, Santa Clause etc.?

Attending a birthday party

Q: I know birthdays are not halal but if a close person invites me, I need to go. So if I went to a birthday party where there is no music, only relatives and close friends, I will not eat the cake but it seems bad if I don't eat the food they ordered, so if I eat the food will it halal for me? Only to eat the food.