Hi Kate
A problem, indeed, my lovely
There's one thing you can do, as i see it......firstly even though your baby is due on the 27th and as long as you're not booked for a caesarian, he could come anytime in mid to late December, even into January.
You can politely let mum know that as a result of this, and that you'll be so busy at that time, you'd like to get settled in first before having family over, as you would be so tired.
But suggest to her to come over to visit and see her grandson, a few weeks after the baby is born and that way, it gives you a chance to get used to the joys of motherhood without worrying about looking after mum too, especially as it will be Christmas.
Your OH is right and i would agree with him on this......It is so special when you have your first child, any child come to that, and you need the time to settle in.
(I have 4 children.....youngest is 8).
I wish you all the very best, Kate and congratulations to you and you're partner.
love from yogi bear xx