Is their relationship really is proper? I know they group up as brothers but at the same time they knew they aren't real brothers, at most they grow up together but still is seen by others as normal brothers, A also think of that (well maybe deceiving himself a lil).
But it is shown that they love each other (idk if its JUST familial love in A 's case but his brother realized his early on)
Her words being "food" than "mom"