My sister lost her pregnancy, but my wife is pregnant and so are several of my friends. Help with how to approach their grief?

My sister had an ectopic pregnancy 2 months ago that was terminated. She nearly died in the process, and it was a traumatic and sad experience overall. We found out last week that my wife is pregnant, 3 weeks after I found out my best friend's wife (both close friends of my sister and her husband) is pregnant. Yesterday I found out my oldest childhood friend's wife is also pregnant. Theyre family friends that predate my sister and I entirely, theyre like family to us. Basically, all 4 got pregnant within about a 10 or 12 week period, but my sister lost hers. My sister doesn't know about my best friend and oldest friend yet either.

I'm afraid of what this might do to my sister and her husband's mental health, and I want to be available to them through their grief while preparing and being excited for my child. They already didn't call us for a week after they found out about our pregnancy, and told me openly it was because they were feeling pretty terribly about losing their child. Shes also still likely got 6-12 months of intense hormones from her pregnancy which will exacerbate the emotions she feels. She wept in her office for awhile after finding out we were pregnant. I have absolutely no hard feelings about this whatsoever, I'm not in slightest upset at them, it feels like the greatest cosmic injustice of all time and it didn't even happen to me. I'm just quite sad for what might have been, you know?

I suppose I'm just curious what points of view you guys may have, or even better, experience similar to theirs or mine.