The Samsung Tablet 10-inch has the capacity to increase both the size of the text and also the brightness (behind the print). I would strongly advise getting the 10-inch to accommodate your father's vision; the 7-inch might be too small. I love this device and is very easy to use and personalize for your needs. Glad to help you !
I, too, highly recommend the 10.1" Galaxy Tab 2. For someone with limited vision, the extra size and really make a difference. In addition to Logan Rivers' information about font and brightness, you can download Audible.com which is an Amazon company that offers numerous audible books for downloads. If so inclined, you can also buy the companion Kindle book and you can also switch between apps/devices.