We are going something very similar to this except that my husband's biological father passed a few days ago.
DH father remarried years and years ago when DH was very young. DH step-mother never considered him part of "her" family. "Her" family consisted of DH father, their child they had together who is about 5 years younger than DH, and her 2 children from a former marriage (one older than DH, one the same age as DH.)
DH did visit his father and family every month and summer when he was a child. Since he's been an adult, we've had very little contact that DH did not originate. Since they moved many states away 25 years ago, we've only had contact with emails occasionally or at the family reunion. These reunions are for DH's father's siblings and their descendants.
At these reunions, DH and his father converse, then when meal time comes, we usually sit with his cousins while DH father and step-mother sit with their "real" family.
Ok, now to the point, DH's father passed and NO ONE personally made a telephone call to let him know. We found out when my DD saw on Facebook that her half-uncle posted that his father had passed on. (Same thing when step-mother passed 3 years ago.)
We asked half-brother why we were not notified when step-mother passed and he said he didn't know how to reach us. We've lived at the same place, had the same phone number for 36 years at that time. Don't know what his excuse is this time.
Since the funeral will be held in far away state, we don't intend on going. There may or may not be a memorial service locally in the near future. (There was for step-mother and we didn't find out until after the fact, so of course we didn't attend.) My feelings are that we won't be told about this one either. If we do find out from other family members, such as cousins, DH still is hurting and doesn't want to attend. I respect his feelings about this, a cousin has said that he should go if there is a local memorial service.