I'd recommend starting with the most popular ones on websites like Archive of Our Own. They usually have a good summary that can give you an idea if it's the type of story you'll like.
Sure, She-Hulk is related to Hulk. Jennifer Walters, aka She-Hulk, got her powers because of a blood transfusion from her cousin Bruce Banner, who is Hulk. This connection is a key part of their storylines in the comics.
Captain America would be a great addition. His leadership and moral compass could guide Hulk and She - Hulk when they face difficult decisions. And his combat skills could come in handy during battles.
In many comic versions, She-Hulk gets her powers after being exposed to gamma radiation, similar to the Hulk. But the details and circumstances can differ in different story arcs. Sometimes it's due to a scientific experiment gone wrong, or a deliberate attempt to gain powers.
She-Hulk became She-Hulk because of a unique set of circumstances. Bruce Banner's blood, with its gamma radiation, entered her system during a medical emergency, and that's what caused her to turn into She-Hulk. This event changed her life forever.
Comics usually depict Hulk as stronger than She-Hulk. Hulk's strength levels are often at a much higher magnitude, but it doesn't mean She-Hulk is weak by any means. She has her moments and skills that contribute to her being a significant character in the comic universe.