Numbness from hands to my elbow. Numbness in my shoulders. Especially when sleeping. Hand and finger stiffness. What could it be?

Arthritis. Hand and finger stiffness is commonly associated with arthritis. Rheumatoid arthritis can make people more prone to nerve entrapments. Peripheral neuropathy is also something to consider. You should be evaluated by a neurologist and may also need to see a rheumatologist.
Arm numbness. This could be a central/neck issue if both arms are equally affected. The hand/finger stiffness could be secondary to disuse. It's possible to get bilateral carpal tunnel and or cubital tunnel but less common to have them present with symmetric symptom intensity and time of presentation.