
I spoke to a very experienced breeder of our breed and she said that you should not allow Mum to escape the problem, as really she should sort the youngsters out. Her discipline is likely to be far more effective than yours (with9in reason). she advised not to let Mum away from them so that to get peaxe she will have to lay dowwn the law.
Also as far as is possible the pups both need to be relegated to as low a status as possible, and Mum's should have hers elevated.
Mum should be fed before the pups, and they should have to wait and watch until she is finished. This will mean splitting her meals so that she also gets fed twice a day.
When the pups are fed they must not be allowed to wander away from their dishes to interfere or try to intimidate the other.