I would get your dad to the doctor very soon. There are lots of reasons for swelling of the ankles. It could be venous insufficiency. That is another way of saying poor circulation and would make sense with what you describe. But he also could have blood clots, kidney, heart or liver issues, or diabetes. He really needs to see his doctor soon to understand what might be going on. My personal guess is venous insufficiency but, that is at best, a guess. https://www.webmd.com/a-to-z-guides/swollen-ankles-and-feet#1