Yeah..that happpened to one of my friendstoo..he saw his passed grandfather reflection in the mirror in their own house...there's another story behind why he saw him though...
But if your bro saw ur grandma and he was calm that might mean she's an a very very good place
Gin are the others in other words...
um...God not only created humans, and not only animals, but he created other creatures which we here call gin, and we can not see them, but they can see us, as believed, but you can sense them...
If you ever had a sleep paralysis, or whatever it's called, it is mostly belived that one of them is sitting right on you... not neccesary to hurt you, maybe give you a message or show you a truth, and sometimes just to mess....
i know it seems weird that i know this, but only again, cuz i'm experienced