adjusting pd doses is an art, not a science, but above all, you have to communicate with your father's neuro. can you talk directly to the neuro because if not you have what appears to be a serious gap in your father's medical care if you feel the need to intervene.
what are the directions on the comtan prescription vial? what does the drug information sheet say for comtan and what to do if you experience side affects?

300mg every three hours starting at 7AM is a high dose of sinemet, the neuro didn't want to increase the sinemet so prescribed comtam.

but this is something you need involve his neuro with, and it appears that's not easy?

some neuros don't recommend controlled release sinemet - SINEMET CR - but if your father hasn't tried it that might be a better option than COMTAN