what should i ado ?

Are they aware that you aren't Christian?
Are you dependent on them right now?

>they are the kind of people that think you are bad if you are not christian
That's not a very christian thought
Since you're living with them, you just gotta check regularly if they're okay with your presence ; if you don't you gonna get kicked out. If they're starting to resent you for whatever reason (they shouldn't, Jesus told them not to and she's your sister), accept to go to church to get some good rep. It's an hour a week and christian/jewish mythology can get pretty interesting

They want you to engage in an activity which is part of your culture. You should go and be thankful that your country is not a muslim shithole. Also usually teens and young adults are atheists who also find it painful to step into a church, like it is hurting them or something, if you were a normal adult and if they would ask you nicely, you would go and stick around for that 1 hour pffft it's not the end of the world.

no reason to live with your sister and her husband, and they probably feel the same thing. No one wants their spouse's sibling living together with them. So what is happening is that they are trying to get rid of you by pretending to be following this retarded cult and then bullying you for not walking along. Obviously there's no discussing/convincing them that you don't want to be annoyed about this nonsense, cause you being annoyed and harassed by them is exactly the point.
Move out, become independent.

>living with my sister and her husband
>atheist

OP is clearly underage