Taking the Bendryl is a way to narrow your search parameters. At this point I'd say and EEG and/or a PET scan is indicated. The trick is NOT to give up.Formulate a plan to search for the cause of his tremor. I'd ask him to take an MMPI test to rule out a depressive episode. Often the afflicted person is the last to realize this.

Just hang in there and continue to give your brother the love and support you have already exibited. Remember too, that your observations are vital to his finding out the cause for this. He cannot dispassionately look at things the way you can. You will get an education!!
Warm him up to the fact that trial doses of medications will be necessary to rule out certain conditions.
If I knew where you lived I could recommend a good Neurologist to you.

Charlie, PD Since 1990. DBS-STN on 2002