I agree... have the MRI done. Another thing to do is to get your dads thyroid test results. (TSH, Free T4 and T3) You need to educate yourself as far as what these mean and make sure your dads results are where they should be. You can find alot of help on www.stopthethyroidmadness.com. Alot of older people are diagnosed with depression and/or dementia, when their real problem is their thyroid.
As long as his tests come back within range the doctor will say they are normal. The problem is that alot of people are symptomatic even when there levels are normal. My TSH was 2 when I started having symptoms 0,4-3,5 were my labs normal range.
Wish you the best of luck with your dad, and hope he feels better real soon.
maybe the combo of drugs isnt working or not working together. Since you can get to NY have you been to any neurogligsts and taken any MRI's of the brain? If not start there. Even try another endo doctor or a gastro guy. Wish you well for your dad