I always go to church every Sunday and always see this guy - I refer to him as "church guy" when I'm telling stories to my friends. He always goes with a girl who seems to be his sister and an older woman, most probably their mom. I really want to meet him and know him, but it's really hard because we're in a church. It would be very easy if it's in a club or bar, but it's in a church! I sat once behind them and we exchanged smiles! What should I do?

That's a tricky one...
You could try to sit behind him again. Then time yourself so, just as he walks past you can bump into him, say 'Sorry', look him up and down smile, then you can either say 'hi' and get a convocation going, or just walk away with a smile on your face. :P

If he's interested , he'll probably make the first move. Just takes some guys a while.

Say hi, and introduce yourself. Yes in church! Just be friendly, you don't have to marry him next Sunday, do you?

In Church would be nice!

Next time he looks at you just give a little smile.
There must be events and fundraisers going on in the church, maybe ask him if he's attending any of them or something.

Smile its always an ice breaker, and yes even in church there's no rule that's says you can't smile at others in the congregation.

Failing this an end of the row seat if he's in front could come in handy as he walks by stick your foot out, hell trip over it and you can go to his rescue, and smile and say how sorry you were that you accidentally ( on purpose ) tripped him up, and he`ll "fall" for you all being well, providing he's not too badly injured. LOL Joke.!

Some times cupid does need a shove in the right direction.

I was once told alls fair in love and war, so...

Just go up to him and say Hello.. I think you are the most handsome man I have ever seen in my life and kiss him... JUST KIDDING... Introduce yourself and
Smile.