The death of Ieyasu’s son and wife was not ordered by Nobunaga
As with many other things, this is a story that is recently being shot full of holes and its veracity called into question.
The story that went around was such:
Tokuhime, Nobunaga’s daughter, fought with her husband Nobuyasu, who was Ieyasu’s son. She then wrote a letter of twelve accusations, accusing Tsukiyama-dono (Nobuyasu’s mother) of trying to sow discord between her and her husband, as well as being in communication to rebel with the Takeda. She also accused of her husband of being cruel. She entrusted this letter to Sakai Tadatsugu, who delivered it to her father Nobunaga. Furious about this, Nobunaga ordered the deaths of both Tsukiyama-dono and Nobuyasu. Nobuyasu was ordered to seppuku, and Tsukiyama was essentially assassinated.
The problem with this is its source.
The account of Nobunaga’s meddling was written in Mikawa Monogatari 三河物語. This is recently considered to be a biased narrative, written approximately around the time of the shogun Iemitsu. As it is meant to prop up the budding new shogunate, its contents is dubious. Other Mikawa Monogatari accounts have been called into question, such as Ieyasu’s presence in the Kanegasaki Retreat.
The account of Nobuyasu and Tsukiyama-dono’s cruelty and immorality was documented in Mikawa Gofudoki 三河後風土記. This is likewise suspected of being a Tokugawa propaganda, written approximately in 1610.
The killing of family members is actually considered scandalous if there is no good reason for it. Therefore some sort of excuse needs to be made to explain Ieyasu’s action, lest it becomes a stain in the shogunate’s records. “Excessive cruelty” and “treason” makes for a valid reason for the order of execution.
In accounts that are considered more reliable, such as the diary of Matsudaira Ietada, only the fact that “Nobuyasu and his wife fought” was corroborated.
Even then, some parts of the relevant texts has been ruined, so it’s rather difficult to verify the claim today. It was written that Nobuyasu had a fight with “御xx”. With two kanji damaged, it’s hard to tell who he fought with. It could have been his wife, sure, as her name is usually written as such in documents: 御新造. On the other hand it could also have been “senior vassals” 御家門, “his grandmother” 御前様, or even his mother Tsukiyama-dono 御母様.
In Azuchi Nikki 安土日記 (Azuchi Diary, an earlier draft of Oota Gyuuichi’s Shinchoukouki), it was recorded that Nobunaga only said “Ieyasu should do whatever he wants”. In fact, Oota Gyuuichi originally wrote in Azuchi Nikki that “Nobuyasu was plotting a rebellion, and Ieyasu’s vassals told Nobunaga this”. Later, this was edited out of the final Shinchoukouki, presumably out of fear of the Tokugawa (the “final” edition of the Shinchoukouki would’ve been completed/finalized during the time of Tokugawa shoguns)
It seems like what actually happened was that due to concerns of treason, Ieyasu had them both killed. Nobunaga’s name was thrown in post-mortem as a scapegoat to preserve Ieyasu’s “clean” image.
Ieyasu has been described as a paranoid person, after all, so I wouldn’t put it past him to have overreacted and making a rash decision. After subjugating the Ikkou-shuu (Honganji sect) riot in Mikawa, Ieyasu banned the faith from his lands altogether. Anyone who is a follower of this faith must convert to another Buddhist sect. Later, he launched the Sieges of Osaka over a convoluted offense in the arrangement of words engraved on a bell donated by the Toyotomi.
