Sibling Rivalry: An Improv Story Game
In this game, players take on the role of siblings and friends. You will need some index cards and pencils. You do not need a GM.
In this game, say "yes" or "yes, and" as often as you can. Try to avoid denying or rejecting a suggestion from another player.
Team up into at least two family groups. If you have fewer than 4 players, one person will be an only child. Ideally, play with at least 4 players so you can have two sets of siblings. For example, Joe and Mary might be a pair of siblings who are also friends with Lorenzo, Frederick, and Helena, each of whom is played by someone at the table.
Get an index card and write down your name, age, and who your siblings are. Decide with your siblings if you all have the same parents (half-siblings are ok in a family), and where you live. Do you have any pets? What are your hobbies, sports, and activities (pick at least 2, no more than 4)? Does your family practice a religion? 
At the bottom of the page, write down your school report card for Reading, Math, Social Studies, Science, and P.E. (Gym).
Prologue: Cooperatively describe a typical day for the siblings, how they interact in the morning, whether they go to the same school, and what their relationships are with their parents.
When players from other families are describing their lives, you can make suggestions about their lives. If the suggestion is about anything within their family or house, any of the siblings in that family can veto it.
If there is more than one family, pick at least one sibling from each other family who is either your friend or your foe. You can have more than one friend or foe. The sibling you pick must be someone you would encounter in your daily life-- they must be the same age, sex, or share a hobby or religion with you. If no sibling in the family matches your character, add a hobby that you share with someone in that family.
Scene One: If there is more than one family, separate into "gangs" that match your friendships. These are usually mini-tribes based on activities, age, or sex, but you might also be split based on doing exceptionally well in particular classes ("we're all Mathletes!"), religious affiliation, or simply based on whether you are all friends or foes. It's okay to have your foes in your gang, as long as your siblings aren't in it!
Tell a story together about what a typical day is like for you and your gang. If you are playing kids who are still in school, focus on the free time you have-- after school, lunchtime, or summer vacation. Describe where and how your gang sees each other.
What Happened Yesterday? Decide with the other gangs which gang goes first and which is listening. Have a conversation with your gang about something exciting that happened yesterday. Each person in the conversation can change, add, or deny details. 
When you have finished with the conversation, one person from the next gang describes what really happened. Then switch, the next gang describes something exciting from yesterday-- it cannot be the same event-- and the next gang after them (or the first gang, if all the gangs have already gone) tells what really happened.
Scene Two: For each family, the other families get together and decide on a situation that brings them into conflict. Write the scene prompt on an index card. Some examples:
•	We're getting a dog! Who's going to take care of it? Who will it sleep with?
•	Dad went on a business trip. Again. Mom is unhappy.
•	One of the siblings broke their leg and has to miss out on something. What is it? Does the other sibling get to do it anyway?
•	Grandma is dying. She's really mean, but everyone is crying anyway.
•	There is a party coming up that everyone is going to be at. Why haven't we been invited?
Role-play this scene between the siblings and anyone they want to call in from their gangs. End the scene after five minutes or when you resolve the conflict, whichever is first.
Scene Three:  All the families and gangs are together for an event. As a group, decide what the event is : a picnic, school graduation, court appearance, camping trip, or natural disaster. During this scene, you must confront someone from the other gang for telling rumors, lies, or gossip about what happened in Scene One. Additionally, you must make some kind of overture of conciliation to your sibling about Scene Two, even if the conflict was never resolved.