You didn't ask a question! You wrote some sentences with errors in them. It's not clear if you want corrections, or if you want to know if the idea is correct.
But, to correct them:
If we didn't know you, we would think that you were insane. (But the tense choice is a bit odd)
unless we knew you, we would think that you were insane. (In this one, the tense/conditional logic is very odd - it doesn't really make sense, and I'm not sure what you mean. If you are just making up an example, you should use a different one, or tell us the wording of the example)
His brother speaks much more politely than he does.
His brother speaks as politely as he does.