Hi...sorry for the late reply.
It seems lots going on with this poor boy.
Your aunt's amazing to be willing to make some changes to help improve him. Many would have him pts, depending on one's financial situation or care tolerance.
I think the fibre food should be changed to pure pumpkin from a tin. It should, however, be placed into a glass container to maintain the integrity of it.
Probiotics should be added.
I also suggest that a possibility of ranitidine...it can help with a host of issues, vomiting, diarrhea, etc....but I'd have to find info regarding dosage for the size/weight of the cat..how often, etc.
Changing the water from a fountain might be in her best interests because it takes a lot of effort to clean the darn thing at very regular intervals. It does, however, encourage the pet to drink more. If he does drink from a water bowl...it should be replaced daily or evem twice daily and bowls cleaned before replacing. Highly fragranced soap should be avoided too, and rinsed very well. I wash all the cat's dishes with paper towel.
I'd also change his food...I wouldn't give him raw food or any human food. NO treats, just his hard food used for special treats fed by hand, used for teaching tricks, etc...
We've done research on lots of foods, and the two best dry foods that has agreed with our cat are
Natural Planet Organics
http://naturalplanetorganics.com/
and Performatrin Ultra (different formulas).
http://www.performatrinultra.com/cat/ingredients_grain-free.htm
The reason I like both these is that the kibble is a bit bigger and the cat chews rather than gobbles and swallows.
Has he had blood testing to see if he has any of the communicable diseases most felines can get? as well, any deficiencies, liver, blood, etc?
Did he recently get inoculated? sometimes vaccines given in bulk can overload the immune system. I'd consider a rethink on that issue (I'll comment more later).
Lots of stuff to deal with....it's overwhelming, but there are some things that can be started immediately such as food change. I'd not use what she's using at this point.
q