A. I do not think the two problems ( previous stones and relative surgery and ravenous appetite) are related.
Hyperthyroidism, diabetes mellitus, protein losing enteropathies are common causes for ravenous appetite and possibly weight loss. A blood test and urineanalysis would e useful to recognise the underlying cause and establish appropriate treatment.
A. Wet food has such a high moisture content that they need quite a lot of it get all the nutrition they need. Unfortunately, being wet it fills them up fast but they go through it too.
I would speak to your vet about also using a little dry food, prescription diet for urinary issues. Most clinics sell it there. They come under different names and brands but they should have one there to recommend. I would use wet and dry together.
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