While it's true that some great players have long skinny fingers and seem to control each one completely independently with infinite precision, many others have had to work with less optimal biological toolsets. Exhibit A would definitely be Django Reinhardt, whose left hand was severely burned in a fire in such a way that he only had full use of two fingers.
My advice would be first of all, try learning to play something really simple like a basic shuffle blues pattern using the open E, A, and D strings, something that uses two strings (this seems to describe how to do it). This will get you started just making some music and getting used to the feel of strings, frets, etc. Don't worry about playing it right, just try to make some noises that sound good to you. Also, realize that the "right way" of holding and playing the guitar is really only right for some median subset of the population, so if you're outside that, you can still make great music with the instrument. I used to know a great left-handed guitarist who was most comfortable playing right-handed instruments upside-down, and I've seen people play the instrument keyboard style, on their lap. If you find your fingers just won't get used to "conventional" playing, you could try experimenting with different types of slide styles and or alternate tunings.
More importantly, from what you've described (and assuming you haven't already), it sounds like you could talk to your doctor about seeing an occupational therapist. Such a person would be best positioned to help you to develop your skills to the best of your ability.