My mum wants to talk....again. Serious moral dilema.

Well, my mum wants to talk on Monday evening.  I am guessing that she and dad are planning to book tickets soon to ensure they can be here for the festive period when my sister is due.  I would imagine that she is going to get me to try and commit to seeing them as soon as possible.  This year is so hard, my dilema is on my DH side there will be two new babies this Xmas and there is the added issue that we have recently been told that my MIL has bone cancer and her prognosis is five years.  This means that very understandably she is going to want to spend special family times together etc, and of course that means that I will expected to be there.  Since this prognosis she has become very lucid verbally due to her strong medication and she has been saying certain things that she would never usually do e.g. the comment about me giving her a cute baby.  I am terrified that she is going to say to us that she wants at least one grandchild from each of us before she passes away, and she has already started hinting.  To be honest, to try and reach a  middle ground I might just  try and see my inlaws a couple of days after Xmas, so they have already made a huge fuss about the babies and the others won't be there, so at least we can see them.  Hopefully, if I tell my mum that then the pressure will be off me to see my sister.  I feel a real bitch for doing that but this situation is so hard, as if I want to start getting emotional around them and detracting from the real happiness of the season.  Furthermore, I want to enjoy my Xmas, and not be forced into extremely tough and potentially hostile situations.  Is that so wrong or am I being selfish??