1)The Johnsons 2)Barney,the mailman and 3)Rosie?

Rosie was seen occasionally in CBS episodes paying Hazel a visit. I'm not familiar enough with those episodes to know for certain if the other characters you asked about were *never* seen, but didn't Steve Baxter live some 25 miles away from Hazel's previous residence? That's explanation enough in itself for a mailman and neighbors not to be around anymore.

Rosie was seen occasionally in CBS episodes paying Hazel a visit. I'm not familiar enough with those episodes to know for certain if the other characters you asked about were *never* seen, but didn't Steve Baxter live some 25 miles away from Hazel's previous residence? That's explanation enough in itself for a mailman and neighbors not to be around anymore.
Barney and the Johnsons never appeared in season five. They were going for a revamped format and they tried to compensate with some new characters: Millie Ballard played by young Ann Jillian (Steve's high school-age office help), and Mona and Fred Williams as new next-door neighbors. Fred was played by Charles Bateman and Mona was played by Mala Powers. I especially liked Mala Powers portrayal of Mona, which kind of reminded me of Edna Skinner's Kay Addison from Mister Ed: an attractive, sarcastic older friend for the young, blonde Barbara Baxter.