Hi. MedHelp adheres to the position of the CDC as well as the input of expert physicians that HIV is only transmitted through unprotected vaginal or anal sex, the sharing of needles, or from mother to child. Simply being around an HIV+ person is not a risk. HIV is inactivated by air or saliva. Therefore, no. Your girlfriend is not at risk living with her brother nor are you. We wish you the best.
As long as you do not have unprotected anal sex with the HIV+ brother and you don't share drug needles with him then you will stay HIV free.