When you vent, we all benefit.
I think the following is correct because you're addressing plurals, not possessives. But tell me if I'm wrong. Thomas' dog ran right in front of the car.
I hope it wasn't a nasty vent.
Thomas' dog . . .
There is a teaching that says this is correct. I must humbly disagree.
When you are referring to something belonging to Thomas', as in Thomas's dog, there is another syllable. Hear it? Thomas. Thomas . . . s dog
. Therefore, there should be an apostrophe AND an 's' to show possession.
If there is no difference in the way it's pronounced, then NO "s." As in Jesus'. Or Moses'. You wouldn't say Moses - es sandals. Or Jesus - es cross. Is that clear as mud?
If you can comfortably SAY the extra "s", then it must be added.
So it would be Charles's. Thomas's. Les's. Amaris's. (My daughter!) The boss's.
But Jesus'. Moses'. Ulysses'.
I'm saying pronunciation is the key as to whether you add an apostrophe OR an apostrophe and the letter "s".
This was the rule when I went to school and the last time I referred to Strunk. Checking my old standby Correct Writing
by Butler, Hickman, and Overby right beside me also says this is correct.
Thank you for asking, although I dread this question coming up because of the overwhelming belief that it's correct to "just add an apostrophe to any word ending in 's' to show possession."
Another one of my soapboxes.