Should I be concerned about my younger brother's Christian homeschool program?

He's a 20-year-old high school dropout. He started dating a girl from a religious family. He decided to enroll in this girl's homeschool program. They are teaching him weird things like Catholicism, Mormon, and JW are a cult. They taught him that Catholic nuns are the demographic with the highest abortin rates. That Catholics invented no meat on Fridays because they own the fish markets. Should I be worried? He also complains to the girl's father about me being an Atheist. He happens to be a minister. He has encouraged my brother to distance himself from me.