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?

Yes, you are right. Good for you!

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!

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 wives's.

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?

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

Yes, you are correct. The use of the possessive 's can be confusing, but it follows a general rule. When a singular noun ends in 's', such as "brother," you add an apostrophe and an 's' to indicate possession. For example, "my brother's house" means that the house belongs to one brother.

On the other hand, when a plural noun ends in 's', such as "brothers," you only add an apostrophe after the 's' to indicate possession. For example, "my brothers' house" means that the house belongs to multiple brothers.

To summarize:

- Singular possessive: add 's after the noun (e.g., my brother's house)
- Plural possessive: add only an apostrophe after the plural noun ending in 's' (e.g., my brothers' house)

Remember to pay attention to the number of owners (singular or plural) when determining whether to use an apostrophe alone or followed by an 's'.