Isn't that the guy that was here yesterday?. You missed out one that.You need to specify the guy with "that" and also "that was" HERE "isn't this the same place that we visited last year" it is best to imagine it, as if you were pointing at or to them and also the thing you are talking about. "isn't he the guy that was here yesterday" may be how to say it. But using two that's is also another way you will hear it spoken.

Neither. You need to combine the two. Correct: Isn't he the guy who was here yesterday? "the guy" is the object of "isn't" [he isn't the guy]; "who" is the subject of "was"