Basically, you just need to put たち (tachi) or ら (ra) with a pronoun
ex
かのじょたち or かのじょら (kanojo tachi / kanojora) - "They" for females
かれたち or かれら (kare tachi / karera) - "They" for males
あのひとたち (ano hito tachi) - "They" for both groups
In your example, assuming that you are talking about a group of mixed people, you could say
あのひとたちはほんとにすごかった。(ano hito tachi wa honto ni sugo katta)