Leia, who uses her latent Force abilities to communicate with the rancor. The beast turns on its masters and eats Jabba.
LOL. I like this.
Overall, I like your plot. However, I don’t like keeping Leia as Luke’s sister; it’s a bad idea which should just be discarded. As for the Luke/Vader/Palpatine conflict, I’d personally go a grayer route. Luke goes with Vader to see Palpatine with the intention of slaying the emperor; any attempt to sway Vader from the dark side is a secondary objective. I also wouldn’t show Vader as a redeemed Anakin. IMO, Vader has committed, ordered, and been compliant with too many war crimes for a single decent act to absolve him of his guilt. The farthest I’d go is showing Vader as a haunted Force ghost, still bearing his wounds in life, who’ll have to earn redemption in the afterlife.