This is also something that's always confused me. Let's use guys for the example. I know that to show possessiveness of guys, you would make it guys' (e.g., Your guys' soup is getting cold). However, my question is how possessive words like this are pronounced? Using the example above, would it pronounced the same way as the regular plural guys (e.g,. You guys are awesome) or guyses? Your guys' (guys) soup is getting cold. Your guys' (guyses) soup is getting cold. Discuss.
Your soups getting cold. Adding in guys doesn't work. I don't think guyses is proper grammar anyways.
As Rainshine said, your example sentences seem grammatically awkward to begin with, so it's difficult to really define with that example. Here's a better example: "The board members' chairs were faulty." Now, it sounds like your question has to do with the pronunciation more than the written form. I tried to do some research to get you a concrete answer, but the only things I could find were discussions, not concrete rules. In my opinion, I believe adding the extra "-ez" sound adds more clarity to the listener, especially if they can't see the written form. In most cases, it would be otherwise too ambiguous to distinguish between plural and singular.
There's no need to add the -es sound. It's spoken word, and I've always been told that the -es sound is wrong. If you make your sentence sensible, it's fine. And you have to know that there's context during conversation.
Hm, I see. Perhaps this would be a clearer example, which is in regards to names that end with S. Carlos' (Carlos / Carlos-es) hat got wet. We could compare it to this, which only has one sound / pronunciation. Arnold's (Arnolds) hat got wet. I did read what you said about the extra -ez, but I'm not sure if the same would apply to names.
While written rules are important, what's most important is to make sure the meaning gets across intact. So it should really be judged on a case-by-case basis. Just say whatever naturally sounds right to you. I really hope you don't sit there for a few minutes contemplating how to say the word. I assume you just say it however you want to say it and move on with your life.
I don't. It really isn't difficult at all to realize whether they'll understand or not. If you're just starting a new topic, you might need to specify. But if you're already in discussion then there's no need to sacrifice being correct when people will understand you anyway.