Whenever any group claims that they, and they alone, have all the truth about God, then an alarm bell should go off in your heart and mind. Christ alone is "the way and the truth and the life" (John 14:6), and His followers are found within countless denominations and churches.
Cults tend to have several characteristics in common (one of which I just mentioned: They claim they alone have the truth, and everyone else is wrong). Cults also often have a strong leader who demands total and absolute obedience; some cults even require their members to cut themselves off from their families. Another characteristic of many cults is that they reject the Bible, or claim their founder's writings are also divinely inspired.
The basic mark of any cult, however, is that it rejects the divinity of Jesus. The Bible teaches that Jesus Christ was God in human flesh that He alone was both fully man and fully God. Cults, however, deny this, and often confuse people who aren't familiar with the Bible by twisting its meaning.
Pray for your cousin, that he will realize he is on a wrong path and will turn his life over to Christ. Down inside he has a hunger for God a hunger that can only be satisfied in a lasting way by a personal relationship with Christ. Make sure also of your own relationship with Christ, and "always be prepared to give an answer ... for the hope that you have" (1 Peter 3:15).