crucifer,
In 1Ac, "the one choosing" is a definition for a treated form of one of the other across clues. That leaves the clue as "Master, second matron". Take the common one-letter abbreviation for "Master" and add a five-letter word meaning "second" (think of "the first or the second" as meaning "the one or the -----").
I'm at the vexing stage of having done a full grid, worked out the two nine-letter words, noted the hint to the location of the quotation and identified the two characters, but the final penny hasn't dropped so I'm still missing the quotation. Time for a break, I think.