The walls in the story are full size television screens that, in the Montag household, there are three full size walls. Mildred wants to get the fourth wall so that she can be surrounded, as she watches interactive tv, by the family.
"All Mildred needs to make her life complete is a fourth TV wall, so she can be surrounded by the characters she watches and interacts with everyday in her living room."
The family are the actors in the soap opera like stories that Mildred watches and actually gets to participate in, like a guest on the show.
"Literally not just one wall, but so far three! And expsneive too! And the uncles, the aunts, the cousins, the nieces the nephews that lived in those walls, the gibbering pack of tree apes that said nothing, nothing and said it loud, loud, loud." (Bradbury)
"You can’t rid yourselves of all the odd ducks in just a few years. The home environment can undo a lot you try to do at school. That’s why we’ve lowered the kindergarten age year after year until now we’re almost snatching them from the cradle."
In this excerpt, which is really very long, Beatty is explaining to Montag how the whole of society changed and how the firemen came to burn things, like books, instead of putting fires out. Beatty is explaining to Montag how books are like a loaded gun in a house which leads to unrest in society.
In this society, everyone is equal and therefore, books are weapons that disrupt that order. So what Beatty is trying to say, is that even though the government has outlawed books, there are still some people who have them, because it is difficult to change a society, heredity and environment effect the way people think.
That is why the firemen go out on calls to get rid of books, when fire alarms are called in to remove the threat that books pose to the society, the last hangers on who still think that books are important.