Well ho often is your DH calling them and asking about stuff? I mean you found out about SIL's wedding a month later... does that mean you DH had called during the month of silence and said 'so anything new?" and got told "nah, same old, same old..." or does it mean your DH is so far out of touch with his family that he'd went months without speaking with them? Same with the baby - did he know she was pregnant? If so, was he calling 3 weeks before the baby was due "hey its getting close now!" or was the total pregnancy a surprise? And if it was does that mean he hadn't called her is 9 months either?
Why is it all on them to call him and tell him and not on him at all to pick up his phone and ask how their lives are?
Don't get me wrong - I don't call my brother, and he doesn't call me - I think that kind of relationship is perfectly acceptable. But I certainly am not complaining that my brother isn't calling me with news, as I have no desire to start being obligated to call him - because it is absolutely a two way street.
DH does try to call them every few weeks, but most of the times FIL doesn't answer the phone. Apparently he's always been bad about that. They do keep in touch through FB messages (which are private) on a regular basis, so I'm not sure why FIL doesn't even send a FB message to let DH know if something important has happened.
SIL and DH text each other fairly frequently, maybe a few times a week. We did find out when she learned was pregnant (via FB of course) about 5 months ago. She was not married at the time (she had only been with the father for a few months at the time). She got married after that, despite saying she had no plans to. So we had no heads up to that either.
So, DH does stay in contact (or tries to anyway), but FIL and SIL seem to like making surprise public announcements.