Help please - "Bob Banner Associates" - Where are they now?

There are quite a few people here who have expert knowledge. I'd like try if anyone can't help me with this question.
I'm trying to track down a rare pilot at ABC/Disney, but they ask me to show permission from "Bob Banner Associates". (Not sure if it's even strictly needed, but I guess they want to be legally on the safe side.)

But he himself died, as was mentioned on this forum too: Bob Banner Dies at 89; Producer in TV’s Infancy

His sons (Charles/Chuck and two others) took over. But it's quite hard to find any current info. I even sent a letter to a last known address. But no reply.

If anyone can pass on a message, or has another clue, that would be extremely welcome!

 

If the actors/writers guilds don't get back to me, then yes, worth a shot! Thanks!

It sometimes all seems so terribly complicated, just to even get an answer to a question.