I used to think Sean looks more like him. But actually he is very much a combination of both his parents. As is Julian, too. But I think Julian looks more like John.
Interesting enugh, my mother said to me once that John himself looked a little bit eastern (japanese/chinese)...
so...who can answer, really?
I think if saw more live footage we would see the similarities: face expessions etc.
It's like: I'm told that I'm a spitten image of my mother, but I think my way to behave etc. sometimes brings out the "my dad" in me.