The last name of a family in my story is Mann. The protagonist wants to refer to a police case by using the family's name. So, is it: ...the Manns' case ...the Manns's case I know I could probably get around by simply saying "the Mann case," or something like that, but situation has come up more than once, and I'd like to know the accepted rule. I know the second option is correct if the name ends in "s," but in this case, the "s" is to make the name plural.
It doesn't matter why the "s" is there; all that matters is if it was there already or if it's only there because it's a possessive. If the word/name doesn't end in a sibilant, simply add an apostrophe followed by an "s" to make the possessive form. If there already is an "s" or similar sound at the end, you have the option to either merely add an apostrophe, which then has to go at the end, or add an apostrophe followed by an "s". This means both your options are acceptable, and I think they both make sense, be it grammatically, logically, practically, comparatively and symmetrically.
The approach I like is to base it on pronunciation. If you'd pronounce the extra "s", put the extra "s" in. But if you wouldn't pronounce it, don't put it. So, if you'd pronounce it "the Manns case", put just the apostrophe. If you'd pronounce it "the Mannses case" put the apostrophe and the extra "s". Now, of course, you have to decide how you'd pronounce it! (I'd pronounce it the first way, so I'd just use the apostrophe.)
' and s. I have an apostrophe in my last name, O'Neil. I named my oldest son Travis. Apostrophes and this use is a common conversation. For my son, as it pertains, we use Travis' for possessive. In the case of the Mann's case... well there you have it. Wanted to weigh in, but have more than just a line to say. Apostrophes. Ha! Mine is a part of my name, but commonly removed by software for everything important.
Oh, I don't think it could be "the Mann's case" unless there was just one Mann. You need the "s" before the apostrophe to make the plural.
The Mann Family. The Mann's family home. The Manns' live up the street. The Manns' can wait patiently. Depends if we are speaking of the family as a single unit or as individuals. A house is singular. The owners, if multiple, would be referred in plural.
Whoa. No. That's... almost completely wrong. I'm with you on The Mann Family. But then once you take the Family away, they're The Manns. Plural, so no apostrophe. The Manns' family home (the family home that belongs to the Manns). The Manns (all of them) live up the street. Apostrophes are for possession or contraction, not for pluralization. Not for random fun.