it's possible that they will get mad and kick you out or start beating u on the reg
or maybe their own son being gay will make them reconsider their feelings
or maybe they will just ignore it and pretend you are straight for the rest of your life
I don't think there's any reliable way to predict how they will react unless you have actually had a sibling in the same situation lol
so honestly I would just take more precautions with ur gay chats and stuff, and don't tell them until you move out on your own anyway
worth mentioning the possibility that they might already know, as well