Saying 'no' to Grandparents visit for Christmas?

I think your in-laws would understand. I understand their feelings of not wanting to visit the days before Christmas and not Christmas day, that would be lame. I don't know if you already said yes, if you did then you should honor that. If you haven't told them yes yet then tell them what you told us, this year is special because it's your first Christmas as a family and you'd like it to be just you guys and next year they're invited to come. I really think they'd understand.