I need help with my family

hey reddit teens. i am having a hard time with my family and friends and i need some help. and also i have a broken hand so im sorry about my horrid typing.

My parents divorced about 8 years ago. this is important later. I live with my mother year round and visit my father often. my mother is a strict catholic along with her family. my stepfather and my sister are christians. i was baptised before i really knew about religion. and in the last few months to a year i came to realize that i do not believe in a god. my father is the same but is more of a relaxed conspirasist type.

I want to know how i can tell my mother/ sister and stepdad that i do not belive and do not wish to be outcasted or forced to go to a church because they will try to guilt me into something. dont get me wrong its not as if im just being rebelious and dont want to participate, i just dont believe in an almighty power.

I have talked to my dads girlfriend about this and we are fairly close even though we only recently met. i just want to know how i can come out to my family and also my girlfriend that i do not believe.

can you help me?