Aaron Carter has now been banned from contacting his twin sister or her family for a year and is not allowed to visit The Grove shopping centre, in LA, where her husband works.
Back in September, Carter reportedly purchased a handgun, an assault rifle and a box of ammunition from a California pawn shop, just days before he allegedly threatened to kill his brother Nick's pregnant wife.
His brother, Backstreet Boys' star Nick Carter, was also granted a restraining order against him.
"I do not wish harm to anyone, especially my family," Aaron Carter tweeted at the time.
However, he has also shown off his weapons on social media.
TMZ reports Aaron must stay at least 30m away from Nick, Nick's wife and kids and other family members.
In a statement released online, the Backstreet Boys singer confirmed he had obtained the order against his younger brother.
"In light of Aaron's increasingly alarming behaviour and his recent confession that he harbours thoughts and intentions of killing my pregnant wife and unborn child, we were left with no choice but to take every measure possible to protect ourselves and our family," he wrote.
On TV, Aaron revealed that he had been diagnosed with multiple personality disorder, schizophrenia, acute anxiety and manic depression.
"I'm prescribed Xanax, Seroquel, Gabapentin, Hydroxyzine, Trazodone, Omeprazole," he told US show The Doctors.
