I suggest you read all the posts that were in response to Ozone Bubble in the last few days. Some of us have highlighted how to change the diet in easy steps. He's making the same transition to health for his dogs right now, so you two could pair up.
The first root to correcting health is the *removal* of what creates dis-ease - and that will start with diet. Adding supplements at this stage may not help but may add to toxity. We are what we are able to absorb - and if your pets have arthritis, allergies etc. they have a lot of toxic waste in them and therefore poor digestion.
I wouldn't be surprised if just by correcting the diet that at least 50% improvement will be noted within 2 months. After that, you can see what needs tweaking in terms of supplementation.