I personally would do it the way you feel comfortable doing it, which is something I can’t tell you since I don’t know what you’d feel most comfortable with. My advice, take them to the side, say you have something you wanna talk about, just come out with it as simply as you can. And avoid saying “I think I’m bi”, because sometimes, when you show people you may have a seed of doubt (with the ‘I think’ they can use it against you. Be firm on who you are, and just say “I am bi.” Then perhaps, let them ask any questions they want to know to dispell their misconceptions about bi people. You can do it one at a time or all at once, depending on which you think would be best.
Also! You don’t have to tell the one who you think would be weird about it! You can just tell the people you’re comfortable with.