Its unlikely that the Coumadin (warfarin) is causing the confusion. But I like your idea that one or more of his medicines may be contributing to his symptoms.
My own approach is to stop as many medicines as possible when an older person becomes more confused. But you cant stop some medicines that he absolutely needs. It would be too dangerous or raise the risk of making other symptoms worse.
In your fathers case, its an easy choice to stay on Coumadin. Hes had a life-threatening condition that requires a blood thinner. And Coumadin isnt usually associated with confusion.
I suggest reviewing all his medicines with his primary care doctor during the next office visit.