Bisexual - Athiest, Christian dad...?

THIS HAS MANY QUESTIONS!

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So like, my life is pretty different from when I last posted. This old dude died who was really close to my dad and I guess going to church really touched him or something and now he goes all the time and has bible studies and its really crazy because it all started in a week. He is now sorta trying to get me and my bro to go to church with him and I'm an Atheist and I sorta feel like he'll make me come with him an I'll be really uncomfortable.

How do I tell him and my mom I'm an athiest?

Another problem is me being bisexual. I have known I'm bisexual for a long time now- even though I'm only 13. I got into some crazy crap last year and my mom found this note about a guy that I wrote that had to be the gayest note ever. And they talked to me about it and were completely okay with it and said they'd always accept me.

How do I officially tell them I'm bi without making a scene?

Another problem with that is that I think my bro is bi-gay too and like I don't want my parents thinking they did some thing weird and raised two gay kids and stuff so...

How do I ask my bro if he is gay/bi?

These are all my questions! Thanks alot!