Is my son who was breastfed one filling time by my aunt considered a brother to her children?

The baby who was suckled five sporadic times by a woman is considered a son/daughter of hers.

Is it permissible for the guardian, or the father of the child to hit the latter in order to teach him/her good manners?

It is permissible for the guardian to hit his/her child for teaching them good manners once they become ten years old provided that it is done mildly, harmlessly and without intimidation. Actually, such punishment is to be employed gradually i.e. after: asking, warning, and scolding. As for the teacher, he isn`t allowed to hit the student unless the latter`s father approves of it, and it is done according to necessity without intimidation, or harm.

Is it permissible for a woman to go out wearing bright colors?

Bright colors are part of a woman`s adornment, and it is impermissible for her to show it to people other than her husband, or one of her Mahrams (Unmarriageable kin).

I`m a cashier at a branch of the Civil Service Consumer Corporation. Sometimes, customers pay more than the due amount. Do I have the right to take that extra money knowing that I cover shortages from my own salary?