Need advise

A group of people showed up a couple of years ago in my small town. I know they are part of something but wouldn't tell. The original couple sounds and looks normal until you try to dig deeper. She is American and he is from india. He goes to some sort of technical school. They own a coffee shop that acts as the center of their activities. The group is very loose in how they connect with other and it is different than how they connect to each other. This is not strange by itself but there is an invisible barrier to get to know them better. They are verse in the Bible and there is always one or two available in the shop to discuss Bible related things. The other day I happened upon parts of a conversation where one was telling another about "the branch" and David". It brought up a lot of memories but almost at the same time, they noticed me, the conversation changed . It was a smooth change but enough for anybody with our past to catch it. I made friends with the indian husband but there is a wall of silence that always comes up. The people who go to their meetings on Sunday (long hours) always seem more "on fire".

Shall I just approach them and ask them if the know the family? That might turn them off to me whether they are or not. Any ideas? They are having a meeting tomorrow sunday again.