I read Alison Weir's book somewhere along the line, it's very solid. Had Millais's very romanticised portrait of the two princes on the cover.
Haven't read Williamson, but I'm sure I can find a copy. I still have my stack card to Emory U. library, even though I took my degree in 1980, and they never throw ANYthing away.
If you'd like a larger book list, re the princes, please feel free to drop me a note in FREEPmail. :-)