The Mother very well could have been protecting herself by participating, idk?
What I DO know, is that IF you are going to discipline, then it ought to be when it happens and sure,swift, consistent, mechanical, without rage...
That is how you 'train' in the animal world and the same psychology applies to humans.
Punishment-Reward System.
Now lets say that hitting with a belt is somehow 'Fair' in that it's carried out with logic and restraint.
The credit I'll give the Mom is she says basically, I want one lash on your behind, turn over, take it and that'll be it.... rather than whipping her until she complies with the initial request.... that is only punishing someone for two things at once, and that is NOT effective psychology.....
I don't think it's right.... Don't get me wrong....
But at least Mom exhibited some integrity in a BAD situation and also kept the belt out of Dad's hands for a while.....
So talking outside of 'right and wrong' I feel psychologically, if you are going to punish with a hit, then it should be clinical at least.
If that is true, the man knew what his wife was doing and stalked out to "get the other belt". But mom did try, I think, to stop the beating before it got really out of hand. It could have been much worse if she hadn't intervened. But I don't know what her intent really was for sure. All I know is that I can't get those images of that girl screaming in pain out of my head.