Sadh and sant means essentially the same thing but are used in context differently. Sadh and sant both refer to a saintly person, one who is in tune with the Guru. But Sadh can often be used as an adjective meaning Holy as in sad(h)sangat -- Company of the Holy.
Giani or gyani means wise or knowledgeable, usually referring to spiritual wisdom. And do you mean Brahm giani? This is a proper noun, a person who possesses spiritual wisdom. And in some Gurbani, it refers to there being only One Brahmgiani. Everything in Punjabi depends on context-- or how a word is used -- so that makes exact translation very difficult.Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=20289Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=20289
Here is a link that gives some support. Gurbani Core Vocabulary