Help for cat Kuzya

It’s very inconvenient to write, but I’ll try ... I don’t already know what to do ... if anyone has the opportunity to help at least something, thank you sincerely!

A little background, my grandmother died, she was from another city, she had a cat Kuzya, a street cat ... his neighbor fed him a month and she was tired, she asked me to pick up the cat, to attach it ... I took it, I found him a room in the shelter, he was castrated there , I thought we’ll give him medicine (fleas, worms) and take it for myself, I have a cat at home, a child, I was afraid of the street news ... The time has come to pick up Kuzya, and our grief, our cat ate the rope, did the operation, rehab ... Kuzyu you can’t take it now, mine after surgery ... they asked the shelter to extend the overexposure, and I found him a house a 65-year-old woman with her apartment ... But taking him from the shelter, it turned out that Kuzya didn’t eat for 1.5 weeks ... the dogs thought he was stressed, maybe he didn’t know the food simply? But he also didn’t eat with the new mistress and just sat under the sofa without leaving anywhere ... she returned it, and he only had bones left, the skeletal is so fluffy 😢 ...
I took him to the clinic, donated blood ... the doctor said that Kuzi had a "broken liver" ... who these rascals are or how it happened who knows ... this is an ordinary street cat ... there are millions 😔
Treatment is needed: injections, force-feeding ... maybe even a liver biopsy ... but I don’t know what to do, we spent a lot on our cat and we still need medication and supervision ... I can’t physically treat another cat. ..then we ourselves will have nothing to do ... but to return him to the street means to find him in painful death ... But to put to sleep, not give a chance to live life, it is possible to recover and be loved ...
Please help save the kitten, I can’t do it alone ... please ... 😢