Should I be worried if they have not been charged yet?

My son and my nephew were in my car with 3 other friends. They were going to buy marijuana. Allegedly, the house where the marijuana was purchased was robbed by the three friends. The three friends, according to the victims, tied them up, forced on the floor at gun point, and robbed them of electronics. The 3 friends were arrested and charged with home invasion. I took my car, son and nephew to the police department after receiving a call from the detectives stating my car was involved in such crime. My son and nephew told the detectives their side of the story. The three friends went inside to purchase. They were only inside long enough to buy. No one ran out in panic and my son stated he didn't drive off in a rush. They only came out with a plastic container of marijuana. The detectives let my son and nephew go with no charges. Both my nephew and son has never been in trouble. They're home from college for summer.