I will be happy for you too! I second the advice to not let them "pee on your parade" so to speak, any baby no matter the number is an amazing miracle, and should be just as exciting.
We are expecting our 3rd baby, who was very much a surprise, and DH family were similar to the poo pooers in your situation. When we announced it to his dad, all he said was "oh, another one? well maybe this one will be a boy..."I just rolled my eyes and ignored it, because we are thrilled, and my family is as well. That was the important part.
*hug* I understand how it feels to have people put down the arrival of a new baby, either in attitude or words, but don't let it get you down, the other ladies on the board and I are thrilled for you