...when Henry and Alice would address the Wilsons as Mr. and Mrs. instead of calling them George and Martha. What's odd is that Martha addresses Alice by her first name and you would think since they are friends, she would do the same. It seems so formal for friends to do. Henry and George would do the same. Henry would always call him Mr. Wilson, while George called him Henry or on occasion just Mitchell.

Did any other shows do this back then?

I think the Mitchells used 'Mr. and Mrs.' because they were younger than the Wilsons.

I think the Mitchells used 'Mr. and Mrs.' because they were younger than the Wilsons.
I noticed this also, and I thought the same thing about the age difference. Everything was much more formal years ago. Look at the way everybody dressed. In addition, these days many children do not address adults as Mr and Mrs. Everything is much less formal when compared to decades ago!

I didn't see anything wrong with it. It wasn't like they were related. I know a lot of people that refer to their elderly neighbors as Mr. and Mrs. Matter of fact, I don't know anybody that doesn't do that. It's just courtesy, a formal greeting and respect, really.