Have you tried the fantastic rare and second-hand bookshop" Fables bookshop" in Grahamstown (the Eastern Cape):
Fables Bookshop, Grahamstown, South Africa.. Ian Belchin who runs the shop might well know of a book/pamphlet or other sort fo literature which might give you more details about the Alcock family.
How about contacting the two boys, GG (Marc) and Khonya (Rauri)? I think that GG is in Soweto and Khonya is in Zululand, but the best person to ask for thier contact details would be Rian Malan of course, he wrote an article for the Guardian last year about GG and I am sure that he would be the right person to aks if you could get into contact with them. The two boys would of course have excellent first hand info about their amazing and selfless parents.
Hope that this helps
The Alcock family fascinates me too, I think that Neil and Creina are up there with the saints themselves.
Belinda