One rule of thumb is to give your snakes an enclosure where the length plus the width is at least as big as your biggest snake's length. You should add at least one foot to the enclosure's length for each additional snake in the enclosure. This is just one technique, though.

Personally, I think the snake in the bucket would find a way to escape. You might consider drilling air holes in a plastic shoe box or sweater box to use as a hibernaculum since it doesn't have to be nearly as large as the main pen.