Disfigurement was the best Rui Fei could offer his siblings for now. That's because he was considering Ji Yao's feelings but that didn't mean he was going to let them go forever.
Every day in that cage he vowed to slaughter each and everyone who had a hand in his predicament which included this grandfather and great grandmother of his.
Don't misunderstand him when you see him spend time with Ji Yao instead of revenging alongside his siblings. It's because he had a goal in mind. He wanted love as much as he wanted revenge but love came first. Capturing Ji Yao was a priority the rest will receive retribution soon enough.
The two siblings didn't have to lift a finger to achieve this. This torment was enough to pierce the brain and make them suffer till they lost their minds. As soon as the old lady's vision cleared up she saw Prince Rui right in front of her.
