No. That is complete nonsense. You can say 'Good night' (two words) to anyone. In fact, it is probably used more in polite situations and among strangers. For example, a TV or radio presenter will always end a late evening or night-time broadcast by wishing the audience 'Good night'. If you eat dinner in a restaurant, the waiter or owner will say 'Good night' to you as you leave. The key thing to remember about 'Good night' is that it is not a greeting, and is not an equivalent to 'Good morning/evening/afternoon'. You can use 'Good morning/evening/afternoon' at the appropriate time of day when you are either greeting or taking your leave of someone. 'Good night', however , can only be used at the very END of the conversation, meaning 'Goodbye', when you are leaving someone for the last time that day, usually in the evening or night-time.

It can be used with anyone...once it's night time and you are leaving. You can also say "Goodbye" either is fine to use with anyone.

In the U.S. "good night" is the usual way of ending a conversation when it is night time. It is not just for family members. For fourteen years a famous U.S. TV news show, the "Huntley-Brinkley report," always ended with the co-anchors saying "Good night, Chet." "Good night, David; and good night for NBC news." Their competitor, Walter Cronkite, closed with "Good night and good luck." At night, I make the choice between "good night" and "good bye" based on whether I feel that the social night is over or not. If it is a telephone conversation and I say "good night," I am hinting that I don't expect or want any more phone calls that evening.

the moment you go to bed or after dinner you back your room . it's my view.

This would depend on the person, but yes I know I personally and many other people wouldn't say "Goodnight" to teachers, colleagues or people we have just met etc; only to family and friends :)