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How did Tadakatsu, Kageie, Yasumasa, and Tadatsugu die?
There is a legend that Tadakatsu died after injuring his hand from carving. If this story is true, he might have fallen ill from the infected wound. If not true, then presumably he died of age.
It was said that Kageie was executed by Kenshin. The story has it that he had sold a horse to Nobunaga, and Kenshin suspected treason. ETA: This was apparently considered a legend, and the official account of his death is due to disease.
Yasumasa seems to have contracted a disease and died of it. Tadatsugu died normally from age.