Unable to call family member's iPhone 14 after iOS 26 update in Family Sharing group

I gave a iPhone 14 to my son. He has his own Apple ID and I have added him to my family group on iCloud via Family Sharing.

Since updating to ios26, the problem is that myself and my wife (who's also part of Family Sharing group) cannot call him. We can text and Facetime him, but not regular calls. It just hangs when we try to call, so we do not get forwarded to the answering machine or anything. He CAN call us !

Anybody else is able to call him.

So it's very, very weird and I would really like to get this problem solved.

I have updated his phone, reset the network settings, checked the do-not-disturb settings, checked the blocked contacts etc. No luck. I even backed up his phone, erase it completely, still no luck. Contacted all phone carriers, and they don’t see any issue on their end.

Please help :-)

[Re-Titled by Moderator]

Original Title: Issue calling family member