Can i put down my cat to save it from further pain?

Salams. I adopted a kitten 8 momths ago from the street as its mother has left it. We took it to the vet to get it vaccinated and treated. After a months time the kittens belly began to swell and it's fur began to become rough. The vet said, its kidney were failing and brain was damaged. We were adviced to put it down but refused to do so and continued to take care of it. After a few weeks, it lost all its senses. It couldn't mew, hear, feel, taste or smell. It was a completely disabled kitten. We were told again to out it down but didn't since we are not sure if its permissible .We have taken care of it for 8 montjs now and it's condition has become worse. It is urinating blood now and it still won't pass awaynaturally. My question is that if we can put it down to sleep as its condition is very bad.And people at home are starting to get abit sick ecausee of it.