> the 2 hires ended up in disaster with both quitting within 6 months. I am trying to be introspective and understand what our group did wrong

Leaving aside perceived quality of work, can you give more details about what happened, and how your employer interacted with the new hires? It will be difficult for anyone on HN to give accurate input that is not just speculation without more information.

E.g.

* did they actually quit or were they fired?

* did they give any explicit reasons for quitting?

* did they voice any concerns about not being happy in the role to colleagues/management in the months before quitting?

* was there conflict between the new hires & colleagues/supervisors?

* did they get job offers for more attractive jobs?

* did management share your concerns about quality of work being produced by the new hires?

* were the new hires on some kind of performance plan or otherwise notified by management that they were underperforming?

* what hiring process does your org use? Are candidates required to write code during an on site interview?