I Don't think Madara could be Sasuke's Grandfather or Great Grandfather because if Madara did have children he would have most likely tried to give them his Rinnegan and have them pass on his will instead of relying on Nagato and Obito to do his work for him (and they may have also possibly gotten their revenge for how the Uchiha treated Madara meaning Itachi and Sasuke may not have been born). Also I personally don't think Izuna and Sasuke look alike, the only thing they have in common is their hairstyle but Izuna's hairstyle wasn't as spikey and stiff as Sasuke's (in the manga anyway) and their faces look completely different... Izuna looks better and Sasuke looks like his mother, Mikoto. If you are using hairstyle to determine if an Uchiha has directly descended or is related to another, Obito does have the same hair as Madara but aside from that don't have any other genes in common aside from the standard Uchiha genes....