The cats could and would kill a young bp and if not kill maim and possibly kill from an infection. I'm pretty sure that the bp striking at them would only entice them more. Keep the snake in its cage whenever the cats are around or the door is open. When you take it out make sure no cats are in the room and keep the door shut. I would just explain to your parents the way you're going to handle the snake, the fact you'll NEVER let the snake and cats meet and the locked set-up you'll have.