Thanks for the reply. I've considered this. But feel that doing this would bring down their holidays. I'm very appreciate of them inviting me. And the last thing I want to do is have a negative affect on them.

And fwiw, my gf's family is not very religious either. My gf's Mother grew up Jehovah's Witness and never got to celebrate holidays. Now she kind of over compensates for not having holidays as a kid. She's a very nice person and I certainly can't blame her for this.