The commandant of the Alcazar had 2 sons killed by the communists; one was captured in Madrid, and the other was captured in Toledo because (for some unknown reason) the commandant didn’t bring his family in with him (as many other Civil Guards and other refugees did). Perhaps he didn’t think the Alcazar would survive; they nearly didn’t. A similar seige on the northern coast (Gijon) ended much worse, with the beseiged asking a Nationalist cruiser off the coast to fire on their positions as they were overrun (after holding out for months).
I’d recommend “The Last Crusade” for anyone interested in this topic; it really details the causes and first few months of the war, and summarizes the rest.
Eby, Cecil D., The Siege of the Alcazar. New York: Random House, 1965.