Just to show how much of a JoJo fag I am, I can spot differences between them.
Johnathan has smaller mouth and eyes than Joseph
-Joseph's hair is spikier and his chest is more narrower across.
-Johnathan was all about jewelry and baubles, maybe the occasional bandanna. Smaller accessories in general.
-Josephs style was more in his clothes. Multiple hats, scarfs, stuff like that.