In Japanese, talking about family members is more complicated than in English. This is mainly due to the fact that there are different words for mother, father, sister, etc., depending on whether you're referring to your own family member or someone else's.

So, for example, if I was referring to my own mother in conversation I would use 母haha, but if I was talking about someone else's mother, I would refer to her as お母kaaさん.

It is important to note that this rule applies only when speaking with a non-family member. It is perfectly natural to call one's own mother お母kaaさん when addressing her directly. You can think of it this way: just as you do not use the polite suffix -さん when talking about yourself, neither do you use the polite form when speaking about your own family.

Another point worth noting is that when referring to your family members with the plain form, you do not need to use 私watasiの(my) or 私watasiたちの(our), as this would be redundant.

Below is a list of the different family words in both their plain and polite forms. Some words, however, do not have a different plain and polite form. For these words, simply use the suffix -さん when talking about someone else's family.

English	Plain Japanese	Polite Japanese
father	父titi	お父touさん
mother	母haha	お母kaaさん
older sister	姉ane	お姉neeさん
older brother	兄ani	お兄niiさん
younger sister	妹imouto	妹imoutoさん
younger brother	弟otouto	弟otoutoさん
parent(s)	親oya	親oya
(both) parents	両ryou親sin	ご両ryou親sin

The ご that you see in ご両ryou親sin is an honorific similar to お in for example お店mise. The difference is that お is used in front of words that use an originally Japanese, or 訓kun読yoみ pronuncation, whereas ご is used in front of words that use pronunciations that are derived from Chinese, called 音on読yoみ.

Breakdown of otousan

Usages of otousan