My sister and I were brought up in the 1980s, when smacking bottoms was still widely considered an acceptable form of child discipline, and our parents divided absolutely the roles involved in this process.
Mum was definitely judge and jury. When we played up, it would almost always be her decision, and hers alone, that determined whether we got a spanking or a lesser punishment, like being sent to bed early or being kept in, grounded in modern parlance.