When I have had extemely ill animals and having to force feed them, I used some Rice baby pablum made into a real thin paste with water. Then squirted it into their mouths. I used a small syringe and only a small amount at a time, feeding a dozen times a day if they would take it.
After doing that for a couple of days, I added some pate style animal food, and slurried it all and force fed until they either started looking for more food, again using the small syringe, or I had to elect to put them to sleep.
Your kitty sounds very ill, I am sorry to say.