So it seems that strictly speaking Angela is the protagonist's stepmother and also Minami's adoptive mother.If you've checked the mobile info, it says Angela's age is 35 (the protagonist is 25 when the game begins). And it's implied Dylan, the protagonist's father divorced his previous wife and then married her (and they must've adopted Minami before she turned 8 or 9, that's another implication since her age is 18 when she's introduced).