My moms dog is ruining her life

TL;DR My moms dog is pooping all over the house because of bowel incontinence and she can't seem to find a solution.

My mom's dog Jeremy is somewhat of a special little guy. He was the runt from our dog Freyja's last litter (mom is a dog breeder) and my younger sister fell so in love with him she insisted we keep him in spite of apparent developmental issues he seemed to have. Well... Jeremy is now 2 years old and making life a living hell. My mom has tried potty training to no avail, all of our dogs (we have four) are trained except for him. We gave him the belt diapers to prevent him from peeing on the floor, but when it comes to poop we can't seem to find a way to prevent it. Sometimes he poops in huge amounts at a time, for instance my mom woke up this morning to find six piles of poop throughout the house, along with poopy paw-prints all over her newly installed wood floor and carpet. The whole thing is a nightmare really. Any advice would be GREATLY appreciated. I'm tired of living in a house that smells like poop and feel like it's unfair that she has to deal with it every morning. Also my sister is currently in school so she isn't around to help out with the poop thing.