I'm sorry to hear that your fellow is getting progressively thinner and weaker, not eating well, and that his urine is dark and odiferous.
Hyperthyroidism will lead to weight loss, but those cats generally continue to have a great appetite. Because his appetite is off too I think he likely has some secondary organ failure.
It's possible his kidneys are failing, and/or that his liver too is failing.
Cats with hyperthyroidism often suffer from secondary effects on the liver. As his metabolism ramped up he may not have been able to eat enough leading to fats being broken down to support his excess calorie needs. The liver is responsible for that and over time can be overwhelmed with fat metabolism and begin to fail. This is a secondary disease condition called hepatic lipidosis. It can be fatal. Increased bile pigments from liver disease can be behind the dark color and foul odor of his urine. Cats with severe liver disease have abnormal clotting ability, so that can explain bleeding in his urinary tract.
Secondary kidney failure and/or a urinary tract infection can also explain a foul odor to his urine and possible pink tinge.
At this point an examination, some simple blood tests and a urinalysis with culture can give you a wealth of information not only on the possible causes of his condition, but whether his disease process is something that can be handled with minimal stress to him or whether he is suffering needlessly. You don't have to do extensive testing, a mini feline geriatric blood panel will hit the needed high lights with a relatively small amount of blood needing to be collected and a urinalysis should be enough.
Right now your fellow is on a starvation path.
I know that your fellow is a well loved friend and I think these results will be extremely helpful in guiding your decisions for him.
Please let me know if you have any further questions.