Here is what you can do to find the source of the problem:
Check for dairy and vegetable ingredients in the Innova dry.
Make a list of these ingredients and compare it with the ingredients you had in the Purina dry.
I know there are vegetables in the Wellness canned and I also know many cats can't tolerate those.
You can compare the Wellness ingredients with the Nutro ingredients also.
Then look at the whole picture you get when you add up the vegetable ingredients in the canned and dry foods. Dairy and more vegetables than the kitties are used to can add up to trouble.
Also take a careful look at the grains to see if there is a big difference between the old and new food.
Since you are seeing loose stools, the sensible thing would be to cut back on the new foods (or stop them altogether) and find foods with simpler ingredient lists.
Then start from square one. For example, you could try feeding the Wellness canned again and a dry food that doesn't have vegetables. California Natural for instance, and see how that goes.
You may have to give up on the Wellness altogether if this food trial doesn't produce good results either.
While you are doing that you can also use a good probiotic (Culturelle for instance) for a month to improve the kitties' digestion.