I know some iterations make a point to differentiate the type of turtle each one is, but for ones where they look the same, I'm pretty positive it's never brought up, mostly because it's a nothing detail that changes nothing.
There is no version that confirms that they are brothers! The cartoon has a little girl dropping the turtles from a fish bowl into the sewer. Was she coming from a pet store? If you scoop a handful of fish from a tank are they all brothers??
Well, I agree the people getting mad over the question are equally irrational, but ultimately it's a nothing burger of a question. The answer is that Laird and Eastman never presented an answer because they probably didn't think it mattered.
Sometimes things can be fun to talk about. I always thought they were biological brothers. They’re definitely brothers either way though
Turtles don't have birthdays because they don't give live birth, they either have a laidday or a hatchday