I think you are perhaps being a bit oversensitive, and quite understandably, but your sister won't just have you as a friend on FB, the photos will have been for many to see, and there really is no harm. I felt the same many years ago ( pre FB) when I had just miscarried my first, much wanted child and everywhere I went, it seemed, was people with pushchairs, or friends announcing their pregnancies and I felt that it was aimed at me. It wasn't. I hope your husband recovers and that you are able to resume your normal life soon, but meanwhile, you must appreciate that other people's lives don't stop, holidays don't get cancelled because your DH is ill. This doesn't mean your Sister doesn't care, but frankly, cancelling their holiday, or being secretive about it will not contribute anything to your husband's recovery. Best wishes to you and to your husband.