Oh I agree, the vomiting is not at all good. If they are tolerating the new food that's a definite improvement. But I also agree that the effects of a diet change take some time to completely register so, yes, do call the vet on this, because there are likely options the vet would know of that can help with this. There are surely other diets you can feed them that will both take care of the urinary issue and also keep their digestions functioning well.
Also, my understanding is that dry food is not great for cats with urinary challenges. There is a problem of mineral buildup. Not sure if you are feeding them kibble or canned food but thought I would mention this.
