"それは不公平(ふこうへい)だよ" is one translation of "It's not fair". But it all depends on the context and in some contexts, this example translation might not be appropriate.
For your 2nd question, I haven't come up with an answer yet.
This may not be what you are looking for, but we have "ひそひそ". When we say "ひそひそ話(はな)す"、we mean that we are talking very quietly so that other people cannot hear what we are saying (usually because we are talking about a secret or something we don't want others to know).
Hope this helps a bit!