Is it strange that I love doing it with my younger brother
What do you mean "doing it with"?
I'm a bisexual, I love sucking my brother's penis
It's sickening that you'd do sexual things with your brother. You need to seek professional help immediately.
It's normal for older men to be attracted to younger men.
That really depends on the age difference, but it's not normal to be attracted to your sibling. You should find someone who can help you with this problem and stay away from your brother until then. This isn't healthy for you or him.