What are the rules for forming possessive nouns with irregular plurals?

When it comes to forming possessive nouns with irregular plurals, there are a few rules to keep in mind. Irregular plurals are nouns that do not follow the typical pattern of adding an "s" or "es" to form the plural form. Instead, they have unique forms. Here are the rules for forming possessive nouns with irregular plurals:

1. If the irregular plural noun does not end in "s," add an apostrophe followed by an "s" to form the possessive. For example:
- Singular: child
- Plural: children
- Possessive: children's toys

2. If the irregular plural noun already ends in "s," simply add an apostrophe after the "s" to form the possessive. For example:
- Singular: sheep
- Plural: sheep
- Possessive: sheep's wool

3. If the irregular plural noun ends in "s" but has a different pronunciation, add an apostrophe followed by an "s" to form the possessive. For example:
- Singular: mouse
- Plural: mice
- Possessive: mice's nest

4. If the irregular plural noun is a proper noun (a specific name), follow the same rules as above. For example:
- Singular: person
- Plural: people
- Possessive: people's opinions

5. If the irregular plural noun is a compound noun, add an apostrophe followed by an "s" to the last word of the compound. For example:
- Singular: brother-in-law
- Plural: brothers-in-law
- Possessive: brothers-in-law's car

It is important to note that these rules apply specifically to irregular plural nouns. Regular plural nouns, which follow the typical pattern of adding an "s" or "es," simply require an apostrophe followed by an "s" to form the possessive. For example:
- Singular: cat
- Plural: cats
- Possessive: cat's toy

By following these rules, you can correctly form possessive nouns with irregular plurals.