spoilerz 4 part 5!!
I found this theory somewhere I forgot (sorry!) but I read about how DID (or MPD during that time period) worked differently in the jojoverse and as polnareff said doppio and diavolo r literally two different ppl.
unlike actual DID in our world where it's different alters, the jojoverse has ppl with entire new souls and physical appearances.
also doppio is not 33!! diavolo is