I don't think there's any way Boey is making it onto this banner, if only for variety's sake. Celica is very likely a mage, so if Mae and Boey are both in then that'd be three mages in one banner.
Also, I personally don't like Boey lol.
My guess for the banner is Celica, Mae, Saber and Atlas, but Conrad could be the fourth slot instead, idk.