The 47 cm is going to be a bit too small for him. I'm 5'9", with a 32 in. inseam (about 81 cm). My bikes are either 54 cm or 55 cm. You're definitely in the right ballpark with the 50 or 52 cm. The 52 would be a good starting point to try out the fit... But I'm assuming your dad won't be around to test ride some bikes before purchasing?
What kind of riding will your dad be using this bike for? If he's not going to be on the bike a lot, a perfect fit might not be all that important.