if you'd like to bring a little peace and good will to your home, I'd recommend Adele Faber's Siblings without Rivalry. Faber is philosophically descended from the Adler-Dreikurs-Ginott school of thought on childrearing which looks at children's behavior as a rational response to perceived situations, and offers concrete steps to teach children better choices.
To help parents understand the jealousy between siblings, Faber asks parents to imagine how they'd feel if their partner brought home a cute new spouse for them to love and share and care for.
Faber recommends what I call the "fair vs equal" doctrine-- in other words, the doctor doesn't put a splint on a child with the flu, he deals with what each child needs when she needs it.
Faber goes beyond Dreikurs' advice for parents to step out of the way and let children solve their own squabbles, recognizing that can lead to a spontaneous re-enactment of scenes from Lord of the Flies in your family room. Social skills must be taught, and Faber helps parents "step in so they can step out" -- teach the skills, and let the kids work on it on their own.
There are good books on this topic and on more complex rivalry issues, but none top Faber's concrete and down to earth advice for siblings across the range of childhood.
