My children don't communicate very much either. I still discuss what each sibling does or doesn't do however, because I am a parent to both of them. It isn't triangulation, it is being part of a family that even though the bonds seem tenuous at times, is still important to me.
When my son got engaged many years ago I can't recall if I told his sister or not, but she did come to the wedding and was present on that important day.
It is hard work keeping this particular show on the road, but the rewards are there if you keep trying.
Not passing on information is a sure way to keep them apart and yourself equally frustrated it seems to me.