8 days in Donostia-San Sebastian seem a lot for this city, it can be visited in a couple of days maximum. It´s not a beach resort in any way, as our weather is very unreliable and tends to be rainy, so I would spend time visiting Getaria, the flysch at Zumaia, Hondarribia, Pasai Donibane, Tolosa...and on the French side Baiona-Bayonne, St Jean de Luz, Espelette, Ainhoa, etc.
Bilbao would probably deserve a minimum of three nights. From here you may want to visit Getxo and the fishing port of Algorta, Puente Bizkaia, Bermeo, Gernika and it´s Assembly Hall, Plentzia, Lekeitio, Ea, Elantxobe, Elorrio, Oñati, Arantzazu...
(as a comment to previous poster, "pelota" includes several types of ball games, Jai Alai is just one of them (it means "happy game" and it´s played with a kind of basket, while "pelota" is normally played with your bare hands)