Question

I got a little confuse by possessive s

The rule goes that all regular plurals get the ending s' f.e. my parents' house

So then it is my brother's house in singular and my brothers' house in plural?
Writeacher
Yes, you are right. Good for you!
tee
Ok so does my parent's house exist? What about wife-wives? It is irregular plural so according to the rule it would go wife's and wives'? Hmm doesn't the rule say that irregular plurals get the ending 's but it can't go wives's!
Writeacher
Parent's house = house belonging to one parent but not the other.

his wife's house = house belonging to one wife

those wives' houses = houses belonging to several wives

And yes, there is no word spelled <i>wives's.</i>
tee
Yes I got it. But one question remains. If the rule says that irregular plurals get 's and not s' why do we say then wives' if it is the irregular plural?
Writeacher
With ANY plural possessive form, if the last letter of the word is -s, then you add only the apostrophe, not another s. (The same is not true of singular possessives.)

IRREGULAR
child -- child's
children -- children's

REGULAR
boy -- boy's
boys -- boys'

http://grammar.ccc.commnet.edu/grammar/possessives.htm