Food options for a 1yr old basset hound

This our first basset hound and we are on his 4 or 5th dog food since we got him at 13 weeks. At that time he was on purina puppy chow, all our other dogs have thrived on pro plan so we did the switch. He had horrible poops, but his first vet visit he did have tapeworms he was treated and put on simplica trio. About 3 months later he was treated for round worms twice (did a stool test) because he was just always hungry but would poop at least 4-5 times a day. Was treated 2x . After that we switched to science diet puppy, poop was still horrible. Started doing probiotic every morning, was getting better but only with the probiotic. Just switched him to science diet sensitive stomach puppy did better, but currently transitioning him to science diet specialty care, salmon, oats and brown rice and he is now itching like crazy and his poop is back to before, so we are doing probiotic daily again. **sighs** worst part is I already have a mini dachshund with horrible stomach issues, and has had silica stones removed in July. He is currently on prescription hydrolyzed soy by science diet. I am so lost…

Any advice would be helpful.

Thanks, Christine