I am so sorry to hear of the pain and trouble that you are going through. We have lost babies out of respect to their pain and problems. It is never easy. Ginger had arthritis so bad that she could not use her hind legs. After watching her suffer we had no choice but to let her go. Four months later Missy through a clot that destroyed her rear nerves. 2 months later Patches realized that her sister Ginger was gone and just stopped eating. When a 6 lb. cat goes to 4 lbs. in two weeks there is no choice. Yes I’m crying as I write this even though they have been gone for over 6 years. But sometimes you have to love enough too let go. As I said it is never easy and as long as you have a memory they are always with you.
Our vet uses a sedative that lets them go to sleep, then the final injection is given. We have been with each of ours at passing.