I'm sure his family are nice people, just like they seem to you. The problem is that no matter how nice they are now, eventually it will come down to whether you are willing to dedicate yourself to their organization. When you take a stand that is opposite of what they want, they will probably change dramatically. To them everyone is a potential convert. Look up "love bombing" and it might start to make sense.
You are in a dangerous position right now because, as you admit, you don't know much about the bible. That is how they catch people. Educate yourself on their arguments and how to refute them unless you want to get sucked in. Don't think it can't happen, they are very good at what they do. Good luck.