From my reading, UDF 2.5 is supported under Windows Vista/7/8. I have 2 PCs running Win 8 and one Win 7. One of the Win 8 PCs (Toshiba C870-1H2 laptop) is only 9 months old. To me, this implies that UDF 2.5 is (or at least should be) supported by all of them. However, according to Windows File Explorer on each of the PCs, the DVDs are empty - no files, no folders, nothing and all space is free (according to Properties) - ie there's nothing on them.
My interpretation of what you (plural) have been telling me is that you know of no real solution but that I could rip the DVDs individually using ISOBuster (£39) or that I could copy/convert them, again individually, using Nero (£59). At least Nero has a trial version so that I can see whether it works. I am somewhat dubious because none of the previously suggested software has been able to see the data, so why should Nero!
I think that my next step will be to ensure that the DVDs play on a different DVD player - in which case we're back to the "Why won't my PCs see them" question!!!
I do feel that if I have to process the DVDs individually and copy/convert and re-burn them, it might be easier to do it on the Toshiba RD-XV48DTKB, burning then in video mode :-
I know how to do that,
I wouldn't need to buy anything and
I know it works
It all feels a bit like a sledgehammer and walnut solution though