Hey aeria,

Welcome to the Forum. I am so sorry to read about all your terrible experiences and symptoms.
My thinking, (on the same lines as Jomar) is that your hand/ arm/ finger symptoms are related to nerve entrapment and related to your neck base of spine issues.
I also note you have tight stomach muscles (and have ruled out GI tract issues) I just wonder if you would benefit from the use of a Foam Roller. Just lying on it appropriately would stretch your stomach muscles. Tight stomach muscles contribute to poor posture and poor posture may contribute to nerve entrapment by for example Upper Crossed Syndrome. I appreciate you have Ehlers Danlos Syndrome so this may not be valid but working on your neck shoulder area could at least reduce those classic arm/ finger symptoms that are very much associated with nerve entrapment.

Best wishes,
Atty