Okay So basically heres what happened,...
The invisability cloak, Sirius gave it to Dumbledore, who gave it to Harry
Heres where it gets interesting, they did die(duh) only they didnt mean to.
Voldemort came before midnight, they had the wrong info
Which was Peters fault, he told Voldemort they knew, and told the potters that he was coming at midnight
thats how he betrayed them