If three people failed in the same territory
If three people have failed in the same territory, you probably don't have three bad reps.
Before you decide the reps are bad, look at what they inherited. If three people failed in the same territory, I'd start with the territory.
Start with the territory: account quality, installed base, the quota, the comp plan, who had it before. If a good rep couldn't make the number there, nothing you do with the person matters, so fix the territory, the number or the plan first.
Then the person, in this order. Do customers choose to spend time with them? Is there pipeline that exists only because they're here? When they're in front of a customer, can they actually sell? Are they still trying to win? The third question is the one most managers skip, and it's the one that separates can't from isn't. One you coach. The other you manage.
Be careful with the rep who annoys you internally but customers keep calling back. They may be doing more selling than the polished rep with perfect CRM hygiene.
Before you decide anything
Sit with them and go through five real deals. You'll learn more in ninety minutes than a month of dashboards.