Why do you think you were asked? We went through similar scenario, can you bring etc etc, oh, and can you bring ........My daughter asked us to go to theirs (s.i.l plus 3 teenagers) for Christmas day lunch.
A week before the day she asked "could you cook the turkey".........no real problem there.
Then the kids asked "can you do us a ham joint"............no real problem there.
So how come we were asked to go for lunch and it cost ME £30.00 ?