Soupy Saturdays with the Pain and the Great One by Judy Blume, illustrated by James Stevenson

From chapters.ca:
MEET THE PAIN:
My sister's name is Abigail. I call her The Great One because she thinks she's so great. Who cares if she's in third grade and I'm just in first?
MEET THE GREAT ONE:
My brother's name is Jacob Edward, but everyone calls him Jake. Everyone but me. I call him The Pain because that's what he is. He's a first- grade pain. I'll always know exactly what he's thinking. That's just the way it is.
These seven warm- hearted stories will give readers a peek at how a brother and sister relate to each other.