So, now I find out that my older brother has beed DX'd with Whipple's Disease.

which has the key phrase:

'Neurologic symptoms occur in some people diagnosed with Whipple’s disease and can mimic symptoms of almost any other neurologic condition.' Maybe SPMS?

Both he and I have been told for years that we have "essential or familiar" tremor.

Again, a bacterial infection that must be treated with 18-24 months of antibiotics.