What's a precise definition of 人家
人家 has many different meanings. Regarding the meaning in question,


The literal meaning is "that person" or "someone", indirectly referring to oneself like "guess who" in English. This might be the reason you find something passive about it.
It's used by young girls/ladies to address themselves in a cute, innocent or flirtatious tone.
It is informal and only used in colloquial language. 
It's inappropriate for a male to use it in any occasion, even not for little boys, otherwise it's considered extremely feminine in a bad way.
Even among young girls/ladies, not everyone is comfortable with using them. Some only use it in front of their lovers; some find this usage skittish (not in a bad way but uncomfortable to say it herself) and almost never use it. 
There is also regional difference. In Southern China it's more common to see usage between normal friends. In Northern China it's mainly within family (like daughter to parents) or between lovers.
In #3 in your question, the purpose is not to avoid direct conflict, but to play innocent/show weakness in order to gain advantage (in this case, excuse).