My Jack Russell is 4 now and she's always been a puker. The first time she puked was in the car on the way home the day I got her. She's been puking fairly regularly ever since. Lillian, however, never acts sick. She is fine and dandy and all of a sudden she starts smacking her lips. Then she throws up and after that she's fine. Her vet could never find anything wrong with her, and the frequency seemed to change as I changed her food. I mentioned in another post that I feed her Purina Pro Plan for sensitive skin and stomachs and she's only thrown up one time since she started on that food, and that was after being with my parents for a few days and eating their dog's food.
It sounds like there might be something more wrong with your mom's JRT. Have they done x-rays to find out if there is an obstruction in his intestines? If everything checks out I would recommend trying different food, the vets have prescription foods that would probably be a good place to start for a dog having the kind of problems your mom's is having.
I hope you're able to get it figured out, and don't give up on him!