Wherever possible, we would recommend that you ask anyone receiving potentially confidential information to sign up to an NDA. We have a standard template available here which is suitable for investment scenarios.
If you have already signed a Term Sheet with your investors this may include confidentiality wording, so you may not need a separate NDA (though an NDA can still be preferable in some circumstances as it tends to be more detailed).
Note that professional advisors will either be regulated and already under an obligation of confidentiality (e.g. lawyers), or will likely agree in their standard terms to keep company information confidential – so in most cases won’t need to enter into an NDA.