My hands shake when moved from extension to flexion, and head shakes when neck rolled across front. what may be up + what kind of doctor to see?

Neuro or ortho: Suggest a neurologist or orthopedist to assess this set of symptoms. Both can obtain a detailed history and examination to evaluate the issue, and suggest further tests such as imaging and/or electrodiagnostics. The neurologist most likely can do the latter, but both can order these tests if needed.

Essential tremor: sounds like a benign essential tremor. These usually run in families, and are self limited. sometimes when in your neck, they can cause involuntary dystorsions, which classify them as a dystonia. these are treated with botox.