I'd grasp Chiaki's lifted leg by the ankle with my left hand and slowly pull it in, pressing her sole against my clavicle.
Kana's blushing pretty heavily which means she knows her goods are showing. Despite that, she doesn't seem to be retreating so she'll probably be willing to let you cup her once you show how submissive you're being to Chiaki. If not, just buckle her elbow from the inside with your right leg and she'll come tumbling down chest-first onto your free hand.
I'd grab her by her ankle and calf, while sweeping her support foot with my leg, making her topple on the other girl. Then I'd quickly jump on my feet and follow up with a kick to the head as she's trying to get back up.