Serenarules
My hands do not work at the same time. If my right is playing a simple melody, my left is either holding a single note, or nothing at all, and vice versa. Similarly, I am not adept at anything faster than eighth notes, and not for very long.
So you are physically incapable of mastering a virtuoso, or maybe even an average, live performance on your chosen instrument, with no cure in sight. Advice is not going to fix that. I have the same problem, but as a result of being too lazy to do the kind of boring practice necessary, which at my stage of life is probably also chronic and progressive. My solution is to use adaptive devices in order to make music without using my undisciplined neuromuscular system. MIDI sequencing will allow even a gumption deficient like me to create a performance that I could never hope to do in real time. If you are not a good composer, well you are not apparently a very good performer either, and rather than trying to force your body to do what it no longer can, you might put your time into learning to become a better composer and arranger. Working alone with your sequencer will let you choose whatever sounds and musical arrangement you want without anyone else's permission. If you produce a body of work that has value to others, burn it to disc, or take it on the road with a band and trigger the performance of your work from storage, using the coordination that you still have.
Unless you believe that your struggle to overcome your handicap defines you in some ennobling way that makes the frustration worthwhile, or you enjoy the exercise of doing the best you can without expecting to achieve a goal beyond your ability, why not use your still intact intelligence to choose a more productive path?
There is an apocryphal story about the Buddha, who met an old adept who was sitting beside a river.
"Tell, me old man," says the Buddha, "what you are doing here."
"I am sitting unmoving every day accumulating spiritual power, and have done so for fifty years," replied the old man.
"And what power have you attained as a result?" the Buddha asked.
"If I choose," said the old man, "I could stand up and walk across that river," was the answer.
The Buddha nodded.
"For a nickle, I can take the ferry," he said.