Can a man and a woman look like each other and not be related?

no they can't

Of course.

Yes, they can.
For example, they can have the same eye/skin/hair color, they can be the same weight and height, they can have the same hair texture. The more they have in common, the more alike they look.

You'll see a lot more of this in young people. When people get older, their looks can change (for example; signs of aging, makeup, hair coloring and styling, lifestyle choices, and attire/accessories change people's appearances).