Keep yourself as bi till your sure and when you come out make sure there not homophobic crap happends you want to make sure if they don't accept it to keep it silent till your older to be safe.
if there not then you can say: "Mom dad i am gay/lesbian and need to listen to me first.
let them find out themselves......if they come to the conclusion themselves they will more than likely be freaked out
ummmmmm wrong place to ask this question
no one here should be giving advice to someones child