One characteristic of cults is that they strongly believe they alone are right in their beliefs, and everyone else is wrong. Thus they reject the central truths of the Bible that Christians have held in common for almost 2,000 years, and substitute their own beliefs for the clear teaching of Scripture.
Why do people get involved with cults? One reason is because they have a deep spiritual hunger - and for a time, they believe they have found the answer to that hunger. Down inside, we all hunger for God (whether we realize it or not), and we search for something to satisfy that hunger. Some try to fill that empty place in their souls with money, or success, or entertainment, or pleasure, or in any one of a thousand other ways. And some try to fill it with the promises of false religion.
But only God can satisfy our longing - and He has made this possible through Jesus Christ. You see, only one thing separates us from God, and that is our sin. But God sent His Son into the world to take away our sins - and He did this because He loves us.
Pray for your cousin, that he and his family will realize their need of Christ. Let this be a time when you examine your own life also. Does Christ live in your heart, and are you seeking to live for Him every day? The Bible says, "Salvation is found in no one else, for there is no other name under heaven given to men by which we must be saved" (Acts 4:12).