Most wizards didn't know things like Harry. He knew Dudley would live a long time and have three kids. He knew that Dumbledore would die at Severus's wand. He knew Vernon would die of a heart attack at 52, and Petunia would go from cancer at 78. He was young when he started to know things.

Rin never really planned on becoming a familiar. But if it helped him kill his dad, he wasn't complaining.