They are not running 4 generators because they need 4 generators. They’re running 4 generators because the procedure says to run 4 generators. They only need one per reactor, and I’d bet they have a way of cross connecting them to only really need 1 for both. Even if off site power is restored, the procedure probably still calls for them to run. Once off site power is restored, they won’t need them at all.
True, wolfpat. The safety system has redundant “trains”, one of which has the lion’s share of safety-related equipment running. To ensure protection of the decay heat removal and spent fuel cooling systems, only one DG need be functional.