If I am at home alone with maid, and I know that my mother will be out at least for half hour, is that a problem of yichud? Does it help to unlock the door? What if it the same situation but i am home with either my brother or father? What about a six year old sister? Thank You
If you are alone with the maid there is a prohibition of Yichud. Unlocking the door is questioable and should not ideally be relied upon. If the door is left open that would be sufficient.
If you are with your brother or father, there is no prohibition of Yichud.
A six year old girl is also sufficient to take care of the yichud issue.