But just saying you don't know doesn't absolve you of taking a stance on the matter.
If I don't make a claim or take a stance, how would you know ? Let's say I wake up in a strange room that is on fire, with a door to the left and a door to the right. As a practical matter I choose the door on the left, but at no time do I make a claim that it is in fact the exit. Just a practical decision, no claim to truth. While you will find me making certain practical decisions, you won't often hear me announcing truth claims.
Even if you answer this with "I'm not sure", this is essentially the same as saying "they have similar possibilities of being correct."
Sorry, I don't agree, the second part there would constitute a claim.
my brother is 1 millimeter tall or 6 feet tall,
The 1mm answer would be silly of course, but I don't think it makes your argument that I have made a claim. Your argument seems to imply that it would not be possible for me to truly not know the answer to certain questions.