ADVICE PLEASE! My Cat's poop is inconsistant and HORRIBLY SMELLY!

I have two Cats, they are 9 months old, so they are still babies. I have had an awful time trying to figure out what to feed them because of sensitive stomach issues. They both have had issues with diarrhea and mushy poop since I got them, so I am careful with what I feed them. They are currently eating Nature's Variety Limited Ingredient Turkey Formula wet food, and a mixture of the Veterinarian Iams low residue formula with the Nature's Variety Limited Ingredient Turkey Formula dry food. They have been eating this for a couple months and they just can't seem to regulate their bowels.

One day their poop is solid and formed, the next it is mushy and on the verge of diarrhea. It is driving me crazy because they get it all over themselves when it's not a solid formed poop and they track it all over the house!! I am going CRAZY! I had not idea that waiting for my cats to poop so I can wipe their butt was part of the job description. Is there anyone else that has had this problem?? What can I do? Any advice on food that might help regulate their poops?? I am in need of some advice or experience from others. Thank you!

Has your vet first ruled out any issues? Are they up to date with their worming? Loose stool can sometimes be due to parasites so this really need to be ruled out first.

You said they have had this problem since you got them....how old were they when you got them? 

I see that low residue food IS for gastrointestinal issues, so the Vet most have already diagnosed both of them with something, which is kind of odd that both of them would be diagnosed with an issue at so young an age. 

I agree that it really could be some sort of parasite after all.  Have you had their stools checked lately to see if they are clear? 

If they are clear of ALL parasites (and some of them require special PCR tests), then I would switch to a different food.  Can you tell if they've eaten more of one thing or the other on the days with they have particularly soft stools?  I'm just guessing one of the foods is disagreeing with one or both of them.  You might have to start over with a new food, or do a process of elimination.  

Are you also giving them probiotics?  That's helpful for all kitties, but especially ones with digestive issues.

Maybe this thread will be helpful:  http://www.thecatsite.com/t/223743/another-cat-diet-question-cat-has-chronic-loose-stools-diarrhea

First, rule out stuff like giardia, coccidia, and tritrichomonas foetus.  Then try just ONE food at a time.  I have a kitty who developed food intolerance around 8-9 mos old.  He's on Royal Canin Gastrointestinal HE.  Keeps him regular and his poops nice and formed, with low odor.

Our 2 cats had severe bowel problems for several months when we first got them, including blood in their stool. We tried multiple so-called premium brands of wet & dry cat food with no improvement at all. However, after switching their food to 100% grain-free (both wet & dry), everything was 100% normal within 2 days. It was an amazing turn around.

Pete