I agree with MommaD - all those postings about how negative children are, are coming from a deep place of pain in your Sister in law's heart.
I think the way you told them was very appropriate, and considerate. It's not the way you told them, it's the fact that you're pregnant and she isn't. And she tried so very hard for so very long to get pregnant.
I think you should leave them alone in general, at this point. Don't exclude them in things that you would have included them in - anniversary well wishes, birthday cards, etc., but don't keep contacting them right now.
I think there is almost nothing that causes such destructive envy as childlessness. In some women, it just eats at them until they are completely unhappy, and many actually wish harm in their hearts to women who are pregnant.
There is a group called Resolve, a support and information group for couples with fertility issues. If you do succeed and get pregnant, you can't come back to any of the meetings to revisit your old friends who you've shared this challenge with - because frankly, you're not physically safe among them. I have two friends who got pregnant after belonging to Resolve, and they knew for a fact they couldn't go to a meeting and if they did, they would be treated with open hostility.
I'm sorry for your SIL. It sounds like they aren't considering adoption or donor sperm, which would be another outlet.
Best wishes. This isn't about you - you've done nothing wrong.
I wouldn't say I've been oblivious to their feelings. Afterall, I have been extremely close to her during her infertility treatments. And I honestly agonized on "how" to tell them we were expecting. They live out of state. So it was either the personal phone call, or be chicken and let them find out via Facebook announcement with our other extended friends network. I thought, since they are family, it would be insulting and thoughtless to let them find out on social media. So I said. A prayer and made the call. I was very gentle, starting the conversation with how they were doing, and celebrating her promotion, and listening to funny stories about their 2 dogs. All before mentioning they'd have another niece or nephew in August. I honestly couldnt think of a more gentle way to put it. I wasn't expecting to get cut off. I guess I'd like some insight from other ladies who have struggled with prolonged infertility, as to these emotional responses on theirs that I can't personally relate to. Do I waot for them to be ready to reach out to us? Do I ignore them and stop texting them? Or do I keep showong the same amount of desired interaction and caring as if nothing between us has changed? I want to be understanding. I just don't know where to go from here to handle the situation.
It's very clear that she isnt. Why would someone try for that long and spend so much money to only be heart broken every single time and turn around and actually be ok with not having children? They are still hurting and probably don't know any other way to deal with it. I'm not saying that you are wrong to have told them but you have completely been oblivious to their feelings. Give them time. Maybe send her an email or Kettering explaining that you didn't realize and that you had no intentions to hurt her.