My ex in law was this way. Her skin or a limb was always falling off for some reason or another. They just want attention & don't know how to get it. Unfortunately, when it is something serious, noone will believe them.
I know the struggle you are having. stressful, isn't it?
Try doing the same thing - ignore what they say and just go on and on about your great news! I have a grandmother who behaves this way and it's the only way to deal with her and not make me feel insane!
I feel your pain with the in-laws. I love my in-laws but recently I can't stand them. Not even three months ago I had a miscarriage and just a week ago their youngest son's girlfriend just had her baby. Great news yeahhh but the problem is that the numbers don’t add up to be his baby, (he is in the Air Force and living out of state). Well my in-laws wrote an e-mail to the whole family titled "new (last name) generation" I was so hurt. Luckily a paternity test is being done. And still today no apology after my husband told them how I felt about the situation.
In the long run I hope your pregnancy is going well and healthy. The in-laws will come around...we can only hope. If anything your island only has to be big enough for you, husband, and new baby boy.
Best wishes!