It seems to be fairly common in many languages that “brother” simply means a male relative usually in the same age group. Often there was a way to make it more specific if it referred to a brother who was born of the same parents.
That’s my point about cousin, too.
The text did not specifically take pains to specify cousins. Or nephews. Or uncles. It could have. It didn’t.
So AT LEAST it’s arguable.
I have long found it unwise to build any significant doctrine on such shakey evidence.