I can't figure out who's grabbing Beatrix's chest. Could be Quatre, but I'm not familiar with the game.

To me, nobody, she has her arms supporting her body, her breast are pressing her legs, and her legs are bent. Also, looks mopre like a wardrobe_malfunction, because the frills leaves a space between the clothing and her breast.

Practically is normal to see Beatrix be the focus of pranks given her naive personality in game, and the halloween event.