I think that the first witchers didn't have any particular school. First witchers could be trained in the caves near Kaer Morhen (one of them is accesible in TW3, according to Geralt the first Trials had been performed here). After a few generations, original Kaer Morhen inhabitants abandoned it (or died) for unknown reason - and then, those of witchers who obtained the fortress became Wolves, and those who remained faithful to the original idealistic principles of witchery became Griffins.
But this is my personal view only.
---------- Zaktualizowano 17:14 ----------
As for the Vipers - I think their seat was located in
Stygga citadel, until
Ebbing was annexed by the Empire in 1239.