“Deadpool” younger cast members have closed deals to come back for Shawn Levy’s third Installment, Brianna Hildebrand and Shioli Kutsuna are both returned.  Hildebrand reprises her role from the first two films as Negasonic Teenage Warhead, the mutant cohort of Ryan Reynolds’ Merc with a Mouth, with the ability to generate nuclear explosions. Kutsuna plays Negasonic…