Together you have a shared thought pool where you both gain experiences from the other. Your Intelligence and Wisdom modifiers both increase by 2 points and you have a telepathic bond with your sibling within 120 feet. You are able to communicate freely between each other.

You both have a perfect understanding of each other and how to stay in synch while in combative situations. While you are within 5 feet of your Sibling, your armor class increases by 2 points, you both gain advantage on attack rolls and any ally that is also within proximity.

While your siblings are within 5 feet of each other and if they are moving together, you have a base walking speed of 40 feet. When you move a sibling more than 5 feet away from the other their base walking speed becomes 20 feet and you can only use your movement action to move one Sibling on your turn.

The bond you share with your sibling is powerful and can be a benefit or a downfall depending on the situation. While you are within 5 feet of your sibling, any status effect that specifically targets one creature, targets the both of you instead. If one sibling makes an attack or uses an ability to affect its immediate surrounding area, the other sibling can ignore the attack or inflicting status.  

Your character occupies two 5 foot spaces.