Bullying Siblings

Question:

I have 3 boys. The oldest is 12, the middle 11 and youngest 7. The middle child has ADHD. My oldest son is a bully to the middle child. My question is how do I handle my sons when they are bickering in front of their friends outside? For instance, my oldest son and friends wanted to play soccer and the middle one said, “I don’t want to play,” and the oldest makes fun of him for not wanting to play the game and the neighborhood kids make fun also. This is an every other day occurrence. Thanks for your help in advance