Siblings don't have to look alike - they may or may not have similarities.

I am not sure about prey size for your snakes, but the mouse/rat should be about as big around as the width as the snake. I am guessing, but IMO, your BP's can probably eat anything from a hopper to a small adult mouse. It's size, not weight that matters.

We don't breed our own rodents, but most people have them in a separate room from the snakes, but still in the house.

Can you share pictures so we can see these siblings?