APA subsequant citation for two different studies with same first author and same year
This page from the APA says to just write them out with the number of authors necessary to distinguish them on the second and subsequent citations. So, for yours, I think you would do: (John, Tom, and Harry, 2014) and (John, Gary, and Frod, 2014). Since the second name is enough to distinguish, you could stop there, but "et al." and just listing the third name are equivalent, so you list the name.