> "you fail them" can mean both "you give them a failing grade" and "you fail to provide the support they need", right?

Yes, but as written the latter would not be a reasonable parse. For that sense: “you have failed them”, sure; “you are failing them”, sure; even “in acting so, you fail them”; but “and then you fail them” as an entire sentence would be very weird. The emphasis I placed on “fail” also doesn’t feel particularly compatible with that sense of the word.