Bravest Ferrel Cat / Very Sick

My wife and I have had the priveledge of knowing the bravest little ferrel cat We have ever known.
We are luckey enough to have property that has enough room to help out a ferrel cat colony for the last 15 years, along with volenteers that have helped feed, capture & neuter, and support over 25 ferrel cats over the years.
In all cases but this one, all our ferrel cats have been untammed to the point of maybe a little scratch on the rear while feeding.
In all the cases of a sick or dying cat they simply just went off to the wild to die somewhere as we have never been able to find one that has been missing.
However with this little guy from the day he was born he was abandon by his mother and my wife and i had to care for him daily to keep him alive. We had to clean his eyes routinely, and constantly pick him up and hold and comfort him.
This must have been what allowed this brave little undernurished kitten to allow us to handle him as he grew into adulthood.
Over the years he actually moved inside from the wild to live in the luxury of our home, (smart Too). He wouldn't allow us to catch him unless he wanted us too, but at night when we would go too bed he would jump up on the bed and allow us to pet him, but solely on his terms, if we did something out of order, he was out of there pronto.
This long drawn out set up is not a means to extract sympathy, but to show what an extrordinary journey he has made.
Now he is about 7 and in very serious condition.
It started out with him losing his balance and walking funny, not alot at first but it got increasingly noticeable. At that time he was having a hard time moving his bowels, and got less and less, and the last time he did it was very small and hard.
We were becoming increasingly concerned after his appetite dissapered so we took him to the vet.
Our local vet didn't really have any answers what was wrong with him, so they took him for a couple of days to do blood work etc.
After 3 days we picked him up, he had been on a caffeter, fed him fluids through an iv, gave him a shot of antibiotics, and did the blood test.
As it turned out he had a larger kidney than the other, the white blood cell count was a little high, he was eniemic and not really eating on his own anymore.
We pretty much spent all the spare money we could raise just to do this, and now things have become more grim.
He now is not eating or drinking on his own, nor does he really urinate normally. We have been feeding him a high calorie mixture of cat food from the vet with warm water and feeding him his water several times a day and night thru a hypo, he still after about 10 days has not had a bowel movement, and seems to be very sensetive around his rear. He can barly get up on his own and cries when he's not sleeping. He' losing weight and looks to becoming weaker, although he can still swallow his water and food.
It is tearing us up inside to watch this but he is such a fighter, and his road so long I simply have not been able to give up on him, and been praying for a miracle.
I'm afraid at this point that we are being selfish trying to hang on to him, and are actually harming him by not letting him go.
I am writing because I was hoping there was a cat expert out there that could answer some of these questions as we are now in the dark.
Thank You All for Reading

 

will your vet let you give him fluids on your own?
Does he have an obstruction inside that might be blocking his ability to move his bowels? Did they do any x-rays?