HIV is transmitted primarily sexually, and it can also be transmitted through blood. It cannot be transmitted through saliva, through casual contact, sharing a toilet seat in a public bathroom, sharing food with someone who is HIV infected. None of these are at all put anybody at risk.
HIV is transmitted through bodily fluids such as sperm, blood, and breast milk. It cannot be spread though simply touching the skin of an infected person or touching something they touched, unless it contains one a bodily fluid that HIV can be spread through. There are no reported cases of HIV being spread through urine or feces so toilet seat does not transmit HIV.
There will be a slim chance of the brother be affected because the trait would turn out to be recessive which means the person genes would be carried out without appearing in that person
