Leaving Alia out was a bad idea
One of the most interesting characters that's often overlooked is Paul's little sister, Alia. In the original story, Paul and Jessica got to live among the Fremen with new names for several months before an emergency forced the tribe to have to move, and their resident Reverend Mother was too old and frail to make the journey, leading to Lady Jessica (who had been working with her, due to her Bene Gesserit skills proving useful) to take the Water of Life ritual. To be honest, it was a seriously bad idea all around, and I wonder what was going through her mind to do this, because of the dangers.
It's possible she didn't have much of a choice and couldn't leave the tribe without a Reverend Mother, and if she hadn't done the ritual, the knowledge the tribe's Reverend Mother had accumulated as well as her future plans would have been lost. But unfortunately, the ritual not only caused her to prematurely give birth, but Jessica's daughter was "pre-born" as a result, her mind awakened to adulthood immediately, as well as being able to access the memories of past male and female ancestors. People who knew the Bene Gesserit ways feared she would turn into an Abomination, someone whose mind and body was taken over by a hostile distant ancestor, who would use any Bene Gesserit abilities she had against others (this actually did happen to Alia, but not until she was in her late 20s). So Alia was a strange little girl that scared people.
The original timeline had Paul fighting the Harkonnens for 2 years before the big battle that led him to becoming Emperor. Alia became a pint-sized badass that ended up not only being able to fight at age 2, she killed the Baron herself.
Delaying her birth for the 3rd movie, having a creepy dialogue between her and Lady Jessica, as well as shooting up the timeline to 6 months actually kinda ruins the story. Plus, Paul killing the Baron wasn't nearly as badass as his little sister doing it.
The only thing that's noteworthy about Alia being "pre-born" but not born yet, is we find out what happens to a baby exposed to the Water of Life much earlier in the pregnancy than if Lady Jessica had done the ritual at 7-8 months in her pregnancy. You'd think she would have suffered a miscarriage and had a stillborn child, but nope. Alia survived.