It would help us better understand your dad's health if you told us what diabetes medication(s) he's taking, how much, and when. You also don't tell us what his glucose readings are; fasting and after meals. Really high is pretty vague. After 10-12 hr fast, above 200 mg/dl bad, above 250-300 very bad, above 400 dangerous. His doctor can prescribe the proper medication to help lower his glucose levels. Go see him/her asap.
You can visit the ADA Web page for nutrition and diet suggestions. http://www.diabetes.org/nutrition-and-recipes/nutrition/overview.jsp
My suggestion is low or no sugar and stay away from bad carbs for the latter will jack up his glucose levels. For a list of good carbs vs bad carbs go here http://www.bellaonline.com/articles/art6628.asp