[color=red]a. Harry and Jane were waiting for us. And Pete and John.
b. Harry and Jane were waiting for us. And Pete and John too.
c. Harry and Jane were waiting for us. And also Pete and John.
Can’t these sentences have two meanings?
Harry and Jane were waiting for us, Pete and John.
Harry and Jane were waiting for us and so were Pete and John.
My feeling is that a-c could come up in casual conversation, or maybe for dramatic effect in a novel.
If they were used in that format at all, it would have to be in very casual conversation as grammatically they are not good. To that end, then presumably those participating in the conversation would understand the meaning.