God Bless us, every one!
Bob Cratchit offers a sincere and devout toast. The others repeat it, somewhat ritualistically; they "echo" Bob's sentiments, rather than expressing their own. Not Tim. He is so moved and so devout that he adds to the toast, emphasizing it, but also enlarging it. It is a particularization--"us" is vague, but "every one" is particular. "Everyone" would have been redundant, but "every one" is not. Part of the genius of the scene is that Tim blesses all those present--which happens to include Scrooge, although he is unseen. Cratchit's words are said for the family he loves so much. "Us" is specific, and exclusive. Tim's words reach beyond "us" to include Scrooge, and indeed, everyone.
As for the rhythm and the meaning of the sentence, Dickens had choices:
God bless us.
God bless us all.
God bless us all, everyone.
God bless us all, every one.
God bless us every one.
The penultimate sentence in that list is pretty good. I might have settled for it. But not Dickens. His choice produces a moment when prose turns to poetry. It is genius.