I am Pagan and my husband is an atheist from a devout Hindu family. We celebrate Diwali, Yule and Christmas. Diwali has no religious significance for my husband, as he isn't a believer, but it's a time for family. For me, Yule is the religious festival. Christmas is the big family celebration with all the usual stuff - tree, presents, feasting - though I might occasionally mutter that these are all Pagan things.
When our eldest grandson was a choir boy, we used to go to church to the Nine Lessons carol service. We also went to Midnight Mass each year and took him home. Though not a Christian, I always loved carols. (Husband had no idea what any of it meant but joined in gamely.) Eldest daughter and her family all emigrated to the US in 2014 and I don't think I will ever go to another carol service, as it would make me cry to remember those days.