Daniel, ryan, and sam are friends. daniel is ryan's brother. ryan is sam's brother. sam is not daniel's brother. how is this possible?

So we know that the three boys are friends - Sam, Ryan and Daniel.

We also know that Daniel is Ryan’s brother and Ryan is Sam’s brother.

But the question here is why does Sam is not Daniel’s brother.

Because the answer here is Sam is a girl which makes her a sister of Daniel, not a brother.