I don’t know much about brain tumors but I do know that stuttering at 2.5 is a common age for a developmental stutter to occur, and there’s a genetic component to stuttering so if his brother was stuttering, it’s not atypical that he is too… especially if his older brother’s stutter was not related to his tumor (which I know you don’t know). I’m so sorry for your loss. I can’t imagine how triggering having your son start stuttering now is. I not aware of any perceptual components that differentiate a developmental stutter vs a stutter caused by a tumor. Idk if brain tumors have genetic component either (I feel like they don’t but I’m not sure), but for a statistical standpoint it seems more likely your sons stutter is developmental in nature vs getting a tumor in the exact same area as his brain than his older brother. With that said, that’s just an educated guess. I hope that the MRI comes back normal and send you peace.