My son was about 5 weeks (i know a bit younger than you're talking about) when i had girlfriends over for my 30th birthday lunch (very different to christmas i know...). They did everything for me i just provided my house as the venue, i was a bit hesitant but i had a great time. DS had a 'good day' and just ate and slept. There really is no predicting how bubs will go even knowing the approx age. All i could reccommend is that you don't let bub get over stimulated and try and keep the day as 'normal' as possible for him/her. If things do get a little hectic try and remain calm so bub doesn't pick up on how you are feeling. On these occasions we usually spend the weeks/months leading up to them worrying about how they'll go and the day comes and they handle it better than we expected it.

Hope all goes well with the remainder of your pregnancy, birth and enjoy your Christmas.