The sentence that should be eliminated to get rid of redundancy would be "The group had quite a past history to reminisce about".
Redundancy refers to a weakness in a speech or a piece of writing that presents unnecessary repetition, information that isn't useful or words with the same explicit or implied meaning.
In the sentence I marked, the word "past" is causing a redundancy. When we're being told that there's "history to reminisce about" it's already implied that it's in the past since we can't reminisce about anything else but the past and all history is past.
Hope this helps!
