help me

ok so i have a girlfriend and i dont know how to tell my family because my mom, grandma are scared of people who are gay atau bi (homophobs) my brother says its the devil's work that makes people gay and bi. as anda can see i have a problem.my girlfriend lives in a different state and they dont know her. when she graduate from high school (older then her. so i'll graduate before her) she is going to come be with me. so i have a while till i have to tell my family but i dont know what to do. my dad is the only one who would be ok if he found out i was bi, my dad is cool like that.