Since you're not having the same problem with your wife and daughter, perhaps the issue isn't necessarily with your phone but rather your son hasn't enabled SMS/MMS on his iPhone?
https://appleinsider.com/articles/1...-messaging-through-continuity-on-ipad-and-mac
The issue being, the iMessage app defaults to using Apple's iMessage texting protocol and Apple refuses to permit other platforms to use it. That would be fine if everyone used an iPhone but of course that's not a reality. The iMessage app does however include secondary support for SMS/MMS, the two texting protocols that most other texting services rely upon. It 'might' be a matter where your wife and daughter already have this enabled but your son's phone does not.