Ugh. Sir this and Sir that.
Just use your -san and -sama affixes like normal translators. Everyone knows what they connote, as opposed to "Sir" which sounds so stilted and unnatural.
English does not have functional equivalents for Japanese honorifics, period. Trying to translate things like "Oba-sama" and "Nee-chan" into non-existent English terms just wastes the translator's time and effort and annoys the readerbase.