I am reading a book on Mongolian empire and it says that daughter in law of Genghis khan left the biggest empire to her sons. It talks about how she refused to marry Ogodei's son and then masterminded the plan to win back the empire using Batur khan's. Jochi's son Batu khan got area near Russia. But the biggest piece of the Mongolian empire went to 4 sons of sorghaghtani beki, who were all Khans. So is the claim true? In terms of land area, was there an empire left by a parent for their children bigger than what sorghaghtani beki left for her four sons?
It depends, of course, on how much you could define the British Empire as something the King-Emperor owned, and thus could leave to his son. Certainly, the British Constitution allowed infinitely less power to the monarch than the Mongol rulers inherited.
Ignoring this though, in 1911, a year after the death of Edward VII, the British Empire was ~12 million square miles [1]. The Mongol Empire, even at its greatest extent, was never more than ~9.3 million square miles.
If we take into account the fact that Sorghaghtani did not leave to her sons the empire at its fullest extent, the Russian Empire in 1894, left by Alexander III to Nicholas II, which was a far more absolute monarchy than the British one, unarguably qualifies.
The Mongol Empire's later stages themselves would have qualified, depending on how much you accept the Great Khan's, largely unenforceable, claim to power. Even the full extent mentioned earlier is one that only works when you accept this claim. In addition to this, the early years of the Yuan Dynasty tended not to include much inheritance by the emperor's son.
[1] - https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/British_Empire