As you know from the novel, Vito seemed to have anticipated the possibility of a plot against him by Tess and Clem, which was one of the reasons he kept them apart. But, a dual Donship (Tess and Clem ruling the Corleone family after disposing of the Corleones) would have been an impossibility.
Ntra la porta tua lu sangu � sparsu, E nun me mporta si ce muoru accisu... E s'iddu muoru e vaju mparadisu Si nun ce truovo a ttia, mancu ce trasu.