What is the influence of Lady Macbeth and the witches over Macbeth’s actions?
Lady Macbeth and the witches do contribute to the murder of Duncan in Shakespeare's Macbeth. The extent of their responsibility is ambiguous, however.
The witches certainly tap into dormant ambition already present in Macbeth. It doesn't take much for Macbeth to make the leap from being told he would one day be king, to thinking about how to achieve the crown: assassinate the king. Minutes after he is told that the first of the witches' predictions has come true--he has been named Thane of Cawdor--he is already thinking about assassinating Duncan. He refers in his aside in Act 1.3.138 to a "horrid image" in his mind, a horrid image that "unfix[es] my hair."
Lady Macbeth thinks about assassinating Duncan immediately upon hearing of the predictions, then hearing that Duncan is coming to spend the night at her castle. She suggests the idea to Macbeth, and he does not reject it. Later, however, when Macbeth decides not to assassinate Duncan, she vehemently argues with him and convinces him to go ahead with it (Act 1.7). And Macbeth does.
Both, then, play significant roles in the killing of Duncan. How much of a role they play compared to the role Macbeth plays, is something you'll have to decide.