There is a precedent with the Chris Heune case. Depends on how cooperative the MP is. If she pleads guilty right away, she may get a fine or suspended sentence.
// still the brother should get jail time for perjury //
He has NOT committed perjury which is lying under oath before a Judge. He has simply lied to the police, something which is very common by people trying to pervert the course of justice, which is perhaps what he should be charged with, if anything.