I would rule out medical causes for the change in appetite, at the age of 11 a senior workup (lab work etc) may be a good idea.
If you are not brushing their teeth daily, they may very well need professional cleanings and extractions.
After medical clearance, I would consider Nutrisca dry foods as a base, my senior dog and my dog with allergies do well on this product. I recently tried Orijen and I am impressed with it for my younger dog, it may be too rich for a senior. Check Chewy.com and compare prices.
Can you take them out for a leisurely 10 or 20 minute walk twice a day? It makes a difference (in my experience).
PS: Add a splash of water to the kibble, don’t free feed, and take out for frequent bathroom breaks, every 2 hours or at least every 4 hours.
