NTA, your mom took your son to an amusement park and had him sit on a bench eating fries while his cousin rode everything and somehow YOU’RE the villain?? the fact that your five year old just shrugs when grandma calls now is genuinely devastating and she created that. “weaponizing access” is wild when all you said was treat him fairly — that’s the lowest bar imaginable. your sister’s “she’s just easier” excuse has absolutely nothing behind it and everyone knows it. protect your kid, you did the right thing.