Perhaps you can share the news more "gently" using words like memory issues? I have seen the whole range over my lifetime as a family member and caregiver.
Also, they deserve to know if they are in contact with him.
Divided or estranged families are a whole 'nother issue beyond my experience.
I have dealt with family with Alzheimers, Lewy-body (usually with Parkinsons) and cognitive issues without a specific diagnosis since my teens. Everyone close knows something is wrong, so please be open about it.
Those on the "outside" can be told too, but be prepared for lots of advice, and in some cases, denial.
Right now, a family member is sharing this info and graciously saying "thanks for keeping in touch, we are doing our bext"