For a singular noun:
* i'n - This is the most common translation and works for most situations.
* i ni - This is more formal and used for emphasis.
For a plural noun:
* i'n - This is still the most common translation.
* i ni - This is more formal and used for emphasis.
For a place:
* i'n - This is still the most common translation.
* i'n nhw - This is more formal and used for emphasis.
For a specific person or group:
* i ni - This is used for emphasis and is more formal than "i'n".
Examples:
* To our house: i'n tŷ / i ni'r tŷ
* To our friends: i'n ffrindiau / i ni'r ffrindiau
* To our country: i'n gwlad / i ni'r wlad
It's important to consider the specific situation and what you're referring to when choosing the correct translation.