I think some are being very mean.
OK so OP is being a bit U, but she is panicking a little.
I think actually this could be a great thing for your family!
They will meet the baby, and then they will travel. By the sounds of it they don't seem overly supportive, so better they are half way round the world than letting you down. FWIW, I DO think they are a little insensitive, but this could be down to the fact that my own DM, her H decided last minute to naff off down under when my sister had planned her trip, knowing that my H was about to bugger back off for good to his country. I know she feels guilty about it, cos she hid it from everyone, but doesn't help ME much does it. Never mind, I have been more isolated with a 6m old than I am now with a 5yo.
Your IL will be way during the time you will be getting your baby into his/her routine. They will not be there to make unhelpful comments, or missing when you'd really appreciate them, cor 6m, they will not be around. Their loss, but one that will work out for the best.
More importantly, it will mean that your H will HAVE to take his share of the baby care, as doing it on your own without the father's help is bloody tough. (Been there, done that)
Don't let this get to you, it's not about you, it's about them and the fact that they are putting their needs first. You and your H can do the same! You can be utterly selfish and hog your lovely little one all to yourselves for the first christmas, you can skype the IL on the day if you really need to talk to them.
Believe me, your child won't miss them, and you will be enjoying your baby too, you won't need to trek over to theirs or have them getting under your feet, just you, H and your baby, what bliss!
Look for positives, you can do this, it'll be fine! Why not arrange to go away for Christmas yourselves? seeing as you won't have any obligations to have to spend it with the IL!