Children of Dune by Frank Herbert

 It took forever to read this book.  One reason is that the book is very long (3 volumes) and the other reason is that the book is not very interesting.  It is written by Herbert many years after the second book in the Dune series, "Messiah", and is structured differently, not continuing the original story, as was the case with the second volume.  It happens 9 years after "Messiah", so Leto II and Ganima are 9 years old now, but have the personalities of a thousands of people, thousands of years old.  This has the result of them talking about sex with each other and other people, which is very controversial for 9 year old characters (i.e. prepubescent children), so in the TV versions, they are made older, closer to 18, rather than 9.

Leto II and Ganima are the future rulers of the Empire, however their aunt Alia rules in their stead as a regent, and seems to like power too much to give it up.  The grandson of the former Emperor Padishah, Farad'n is planning to kill them both and retake the throne (rather, this is his mother's plan, the daughter of the former Padishah).  Jessica, their grandmother has aligned again with the Bene Geserit order and is looking into different bloodline preservation, including the mating of her two grandchildren, the brother and sister producing offspring. 

Alia is possessed by the Baron Harkonnen, her grandfather, and one of the many personalities that live inside of her since she was born 'awake' because of the overdose of spice her mother Jessica took when pregnant with her. There is not much love left between mother and daughter, and they are actively planning to kill one another.  Alia is said to be possessed and thus becoming an 'abomination', which is punishable by death.  Baron Harkonnen has intense sexual urges which he satisfies by having Alia have sex with various men on her court.

The fremen are also rebellious and want Arakis to go back the way it was, a harsh desert planet, instead of the increasingly green and watery one, which happened after the Atreides started their teraforming projects.  The result of the planet being teraformed is that the sandworms becoming more rare, and thus spice production and availability becoming less.  Most entities in the empire like the Spacing Guild and CHOAM have huge stockpiles of spice, but are still anxious about where would their future supplies come from.  Several groups are trying to breed sandworms on other planets and thus ensure supply of spice, but these efforts all fail eventually.

 When the assassination attempt on Leto II and Ganima fail, Leto II merges with a larvae of sandowrm (sand trout) and becomes a different type of being, with great strength and resistance to all damage while being able to live for many thousands of years.  Leto II saw in this visions that this is the only way for the human race to survive and continue existing. Leto II eventually is victorious over all the other sanctions, marries his 9 year old sister formally, but informally gives her as a concubine to Farad'n and new era of peace and prosperity comes over the Empire.