With more and more information coming out about the new DC film, Shazam, there are still many unanswered questions. We know the casting for all of Billy’s foster siblings, but probably the one that stands out the most is Grace Fulton as Mary Bromfeld. This is mainly because the rest of the children are either in their early to mid-teens or at least resemble someone of that age, but Grace Fulton is 21 years old and looks that age. Granted they could just play her as an older kid in the Foster home, but even that seems like the stretch. Especially since Billy and Mary are typically portrayed as being roughly the age, with them being literal twins prior to Flashpoint making them unrelated.
However, this age discrepancy could be explained depending on what direction they go with it. Namely, having her take on her superhero identity from the comics, Mary Marvel. Likely Grace’s casting was done with this in mind, regardless of when she’s introduced, since unlike Billy, prior to the new 52 anyway, Mary didn’t physically chance when she activated her powers, only her outfit changed. So likely they wanted to cast someone who would look better next to Zachary Levi’s Shazam. But will we see this happen in the initial film?
It really depends on what source material they adapt. In the Shazam run written by Geoff Johns as back-up story to his Justice league run, the initial storyline ended with all of Billy’s foster siblings gaining the powers of Shazam as well, though for a limited time. We can already tell that elements of the new 52 version of the character are being used, with the inclusion of the other Foster children besides Mary and Freddy be an indicator, though this may be a bit excessive for a first outing. Though having Freddy and Mary gain powers in this first film near the end could possibly work if done well. We already know that Freddy will be the only one of the foster kids to know Billy’s secret initially, but it could be possible that Mary could find out as well by the end of the film, and having these 3 be the only ones to know at the start could be a neat reference to their pre-Flashpoint connection