Actually, we usually DO pronounce the extra 's.' For example, how would you say that Henry James wrote The Turning of the Screw? I reckon you wouldn't say, "Henry James novel The Turning of the Screw. " You'd say. "Henry James's novel, The Turning of the Screw." Wouldn't you? Or 'the Jones's picket fence,' rather than 'the Jones picket fence.' I think it makes sense to actually say it out loud or to yourself, and ask yourself if you're pronouncing the extra 's' or not. If it's too awkward, or there is the possiblity of confusion, you can always re-word the thing. The minister's car, versus the ministers' car, versus the ministers's car? Yikes. I would never say 'the ministers-ezz car,' even though the written meaning of it with the extra apostrophe-s would be clear. More than one minister in that car! I'd probably be more inclined to say 'the car the ministers came in,' or something like that. To avoid the apostrophe tangle. Ain't writing fun? Using the extra apostrophe-s can make the written form more compatible to how we actually say it. I think that's why it's okay—even recommended—that it be used in many (but not necessarily all) cases. Punctuation is there to clarify a situation, really. To make it easier to read and comprehend, both silently and out loud. My personal philosophy is : "Adjust as needed."
I would pronounce those words that way, but we were talking about sisters' (like "sister-ziz"), which makes no kind of sense.
Context usually makes these things clear; both these words are pronounced the same but it's fairly obvious most of the time whether your referring to several ministers or one.
But you'd never write "sisters's", because if the car belongs to one sister, it's "sister's", while if it belongs to more than one, it's "sisters' ". It would only be sisters's if the car belong to someone called Sisters.
Didn’t this all start when you said that grammatically speaking it should be “The Andrew Sisters’s new album”? Well the sisters here is referring to the plural, so it’s The Andrew Sisters’ new album.
Unless you want to get really pedantic, and say The Andrew Sisters is singular ...the name of a singing group. Like The Beatles. I repeat. Ain't writing fun? To make it even more fun: the actual name of the group is The Andrews Sisters. Their surname was Andrews, not Andrew.