The question has arisen whether Robert Oswald and Harvey Oswald looked alike, and I suppose they did, a little. Not to where it screams out "genetics" to you, but I'll admit that if they played brothers in a movie, nobody would balk.
And let's remember that unrelated men play brothers in the movies all the time, and rarely does anyone balk. Sometimes, the physical dissimilarity is ridiculous, such as the three brothers in Bonanza. But, they had an excuse for that: they were supposed to be only half-brothers.
In this case, they kinda/sorta look alike, but close inspection reveals quite a lot of divergence of the shape of the head, the eyes, the ears, and the mouth. The noses look the most alike, in my opinion.
However, again, they could have played brothers in a movie, and surely, you could easily find two other men who looked far more dissimilar and unrelated. But, let's remember: Oswald was chosen for his role precisely because he looked a lot like Robert's brother Lee. And if he looked a lot like Lee, then it's hardly surprising that he looked somewhat like Robert.