I don't think there are any B&Bs close to Alton Towers that could take that many. Most of the B&Bs have fewer than 10 rooms.
You could try for a nearby Travelodge or Premier Inn, but I guess most of these will be room only. Or there are some larger hotels in Stoke-on-Trent and some Holiday Inn Expresses nearby. Or see if you can get a good group rate at the Alton Towers hotels, by contacting the corporate bookings.